diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2744f6bfd..c3bb75015 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -36,8 +36,6 @@ jobs:
       fail-fast: false
       matrix:
         ruby:
-          - "2.5.0"
-          - "2.5"
           - "2.6.0"
           - "2.6"
           - "2.7.0"
@@ -47,7 +45,6 @@ jobs:
           - "3.1.0"
           - "3.1"
           - ruby-head
-          - jruby-9.2
           - jruby-9.3
     steps:
       - uses: actions/checkout@v1
diff --git a/lib/prawn/document.rb b/lib/prawn/document.rb
index 439667d5a..686eb829b 100644
--- a/lib/prawn/document.rb
+++ b/lib/prawn/document.rb
@@ -753,7 +753,7 @@ def apply_margin_options(options)
       end
     end
 
-    def font_metric_cache #:nodoc:
+    def font_metric_cache # :nodoc:
       @font_metric_cache ||= FontMetricCache.new(self)
     end
   end
diff --git a/lib/prawn/document/column_box.rb b/lib/prawn/document/column_box.rb
index dc766893e..5bf74b34d 100644
--- a/lib/prawn/document/column_box.rb
+++ b/lib/prawn/document/column_box.rb
@@ -52,7 +52,7 @@ def init_column_box(user_block, options = {})
     # work.
     #
     class ColumnBox < BoundingBox
-      def initialize(document, parent, point, options = {}) #:nodoc:
+      def initialize(document, parent, point, options = {}) # :nodoc:
         super
         @columns = options[:columns] || 3
         @spacer = options[:spacer] || @document.font_size
diff --git a/lib/prawn/encoding.rb b/lib/prawn/encoding.rb
index 5284352a0..0919bdf20 100644
--- a/lib/prawn/encoding.rb
+++ b/lib/prawn/encoding.rb
@@ -9,7 +9,7 @@ module Prawn
   module Encoding
     # Map between unicode and WinAnsiEnoding
     #
-    class WinAnsi #:nodoc:
+    class WinAnsi # :nodoc:
       CHARACTERS = %w[
         .notdef .notdef .notdef .notdef
         .notdef .notdef .notdef .notdef
diff --git a/lib/prawn/font.rb b/lib/prawn/font.rb
index 6eb4dac94..41281adff 100644
--- a/lib/prawn/font.rb
+++ b/lib/prawn/font.rb
@@ -236,7 +236,7 @@ def save_font
     # ++
     #
     # @private
-    def find_font(name, options = {}) #:nodoc:
+    def find_font(name, options = {}) # :nodoc:
       if font_families.key?(name)
         family = name
         name = font_families[name][options[:style] || :normal]
@@ -257,7 +257,7 @@ def find_font(name, options = {}) #:nodoc:
 
     # Hash of Font objects keyed by names
     #
-    def font_registry #:nodoc:
+    def font_registry # :nodoc:
       @font_registry ||= {}
     end
 
@@ -328,7 +328,7 @@ def self.font_format(src, options)
       end
     end
 
-    def initialize(document, name, options = {}) #:nodoc:
+    def initialize(document, name, options = {}) # :nodoc:
       @document = document
       @name = name
       @options = options
@@ -400,11 +400,11 @@ def add_to_current_page(subset)
       @document.state.page.fonts[identifier_for(subset)] = @references[subset]
     end
 
-    def identifier_for(subset) #:nodoc:
+    def identifier_for(subset) # :nodoc:
       @subset_name_cache[subset] ||= "#{@identifier}.#{subset}".to_sym
     end
 
-    def inspect #:nodoc:
+    def inspect # :nodoc:
       "#{self.class.name}< #{name}: #{size} >"
     end
 
@@ -413,13 +413,13 @@ def inspect #:nodoc:
     # that cache certain values (See
     # Prawn::Table::Text#styled_with_of_single_character)
     #
-    def hash #:nodoc:
+    def hash # :nodoc:
       [self.class, name, family].hash
     end
 
     # Compliments the #hash implementation above
     #
-    def eql?(other) #:nodoc:
+    def eql?(other) # :nodoc:
       self.class == other.class && name == other.name &&
         family == other.family && size == other.size
     end
diff --git a/lib/prawn/fonts/afm.rb b/lib/prawn/fonts/afm.rb
index dabd772b9..a1dcbfc7c 100644
--- a/lib/prawn/fonts/afm.rb
+++ b/lib/prawn/fonts/afm.rb
@@ -44,14 +44,14 @@ def self.metrics_path
           end
       end
 
-      attr_reader :attributes #:nodoc:
+      attr_reader :attributes # :nodoc:
 
       # parse each ATM font file once only
       def self.font_data
         @font_data ||= SynchronizedCache.new
       end
 
-      def initialize(document, name, options = {}) #:nodoc:
+      def initialize(document, name, options = {}) # :nodoc:
         name ||= options[:family]
         unless BUILT_INS.include?(name)
           raise Prawn::Errors::UnknownFont,
@@ -84,7 +84,7 @@ def bbox
       end
 
       # NOTE: String *must* be encoded as WinAnsi
-      def compute_width_of(string, options = {}) #:nodoc:
+      def compute_width_of(string, options = {}) # :nodoc:
         scale = (options[:size] || size) / 1000.0
 
         if options[:kerning]
diff --git a/lib/prawn/fonts/ttf.rb b/lib/prawn/fonts/ttf.rb
index 587093350..7a28a9ca5 100644
--- a/lib/prawn/fonts/ttf.rb
+++ b/lib/prawn/fonts/ttf.rb
@@ -61,7 +61,7 @@ def initialize(document, name, options = {})
       end
 
       # NOTE: +string+ must be UTF8-encoded.
-      def compute_width_of(string, options = {}) #:nodoc:
+      def compute_width_of(string, options = {}) # :nodoc:
         scale = (options[:size] || size) / 1000.0
         if options[:kerning]
           kern(string).reduce(0) do |s, r|
@@ -323,7 +323,7 @@ def embed(reference, subset)
         hmtx = font.horizontal_metrics
         widths = font.cmap.tables.first.code_map.map do |gid|
           Integer(hmtx.widths[gid] * scale_factor)
-        end[32..-1]
+        end[32..]
 
         # It would be nice to have Encoding set for the macroman subsets,
         # and only do a ToUnicode cmap for non-encoded unicode subsets.
diff --git a/lib/prawn/graphics.rb b/lib/prawn/graphics.rb
index a84c6645c..9beea14c2 100644
--- a/lib/prawn/graphics.rb
+++ b/lib/prawn/graphics.rb
@@ -237,7 +237,7 @@ def ellipse(point, radius1, radius2 = radius1)
     #
     def polygon(*points)
       move_to points[0]
-      (points[1..-1] << points[0]).each do |point|
+      (points[1..] << points[0]).each do |point|
         line_to(*point)
       end
       # close the path
diff --git a/lib/prawn/grid.rb b/lib/prawn/grid.rb
index 6dca7c7e1..0b5e48fd1 100644
--- a/lib/prawn/grid.rb
+++ b/lib/prawn/grid.rb
@@ -34,18 +34,16 @@ def define_grid(options = {})
     def grid(*args)
       @boxes ||= {}
       @boxes[args] ||=
-        begin
-          if args.empty?
-            @grid
+        if args.empty?
+          @grid
+        else
+          g1, g2 = args
+
+          if g1.is_a?(Array) && g2.is_a?(Array) &&
+              g1.length == 2 && g2.length == 2
+            multi_box(single_box(*g1), single_box(*g2))
           else
-            g1, g2 = args
-
-            if g1.is_a?(Array) && g2.is_a?(Array) &&
-                g1.length == 2 && g2.length == 2
-              multi_box(single_box(*g1), single_box(*g2))
-            else
-              single_box(g1, g2)
-            end
+            single_box(g1, g2)
           end
         end
     end
diff --git a/lib/prawn/repeater.rb b/lib/prawn/repeater.rb
index bc5b3f010..1d4e4644a 100644
--- a/lib/prawn/repeater.rb
+++ b/lib/prawn/repeater.rb
@@ -83,7 +83,7 @@ def repeat(page_filter, options = {}, &block)
     end
   end
 
-  class Repeater #:nodoc:
+  class Repeater # :nodoc:
     class << self
       attr_writer :count
 
diff --git a/lib/prawn/text/formatted/arranger.rb b/lib/prawn/text/formatted/arranger.rb
index 3b1fbe786..ee1659d2c 100644
--- a/lib/prawn/text/formatted/arranger.rb
+++ b/lib/prawn/text/formatted/arranger.rb
@@ -9,10 +9,10 @@
 
 module Prawn
   module Text
-    module Formatted #:nodoc:
+    module Formatted # :nodoc:
       # @private
 
-      class Arranger #:nodoc:
+      class Arranger # :nodoc:
         class NotFinalized < StandardError
           DEFAULT_MESSAGE = 'Lines must be finalized'
           MESSAGE_WITH_METHOD = 'Lines must be finalized before calling #%<method>s'
@@ -277,13 +277,15 @@ def apply_font_size(size, styles, &block)
 
         def subscript?(styles)
           if styles.nil? then false
-          else styles.include?(:subscript)
+          else
+            styles.include?(:subscript)
           end
         end
 
         def superscript?(styles)
           if styles.nil? then false
-          else styles.include?(:superscript)
+          else
+            styles.include?(:superscript)
           end
         end
 
diff --git a/lib/prawn/text/formatted/box.rb b/lib/prawn/text/formatted/box.rb
index 5948e97f7..16b6b3a4f 100644
--- a/lib/prawn/text/formatted/box.rb
+++ b/lib/prawn/text/formatted/box.rb
@@ -257,7 +257,7 @@ def height
         #
         def draw_fragment(
           fragment, accumulated_width = 0, line_width = 0, word_spacing = 0
-        ) #:nodoc:
+        ) # :nodoc:
           case @align
           when :left
             x = @at[0]
diff --git a/lib/prawn/text/formatted/fragment.rb b/lib/prawn/text/formatted/fragment.rb
index c10ecc17f..3eac70ab7 100644
--- a/lib/prawn/text/formatted/fragment.rb
+++ b/lib/prawn/text/formatted/fragment.rb
@@ -32,7 +32,8 @@ def initialize(text, format_state, document)
 
         def width
           if @word_spacing.zero? then @width
-          else @width + @word_spacing * space_count
+          else
+            @width + @word_spacing * space_count
           end
         end
 
@@ -51,7 +52,8 @@ def superscript?
         def y_offset
           if subscript? then -descender
           elsif superscript? then 0.85 * ascender
-          else 0
+          else
+            0
           end
         end
 
@@ -211,7 +213,7 @@ def process_text(text)
             string = string.rstrip
 
             if soft_hyphens_need_processing?(string)
-              string = process_soft_hyphens(string[0..-2]) + string[-1..-1]
+              string = process_soft_hyphens(string[0..-2]) + string[-1..]
             end
           elsif soft_hyphens_need_processing?(string)
             string = process_soft_hyphens(string)
diff --git a/lib/prawn/text/formatted/line_wrap.rb b/lib/prawn/text/formatted/line_wrap.rb
index bc3b5e4f1..eac14dff3 100644
--- a/lib/prawn/text/formatted/line_wrap.rb
+++ b/lib/prawn/text/formatted/line_wrap.rb
@@ -10,9 +10,9 @@
 
 module Prawn
   module Text
-    module Formatted #:nodoc:
+    module Formatted # :nodoc:
       # @private
-      class LineWrap #:nodoc:
+      class LineWrap # :nodoc:
         # The width of the last wrapped line
         #
         def width
diff --git a/lib/prawn/text/formatted/parser.rb b/lib/prawn/text/formatted/parser.rb
index ee7b85c37..2200e4ff5 100644
--- a/lib/prawn/text/formatted/parser.rb
+++ b/lib/prawn/text/formatted/parser.rb
@@ -100,7 +100,7 @@ def self.to_string(array)
           end.join
         end
 
-        def self.array_paragraphs(array) #:nodoc:
+        def self.array_paragraphs(array) # :nodoc:
           paragraphs = []
           paragraph = []
           previous_string = "\n"
diff --git a/lib/prawn/text/formatted/wrap.rb b/lib/prawn/text/formatted/wrap.rb
index a78f00428..81b4fdac5 100644
--- a/lib/prawn/text/formatted/wrap.rb
+++ b/lib/prawn/text/formatted/wrap.rb
@@ -11,10 +11,10 @@
 
 module Prawn
   module Text
-    module Formatted #:nodoc:
+    module Formatted # :nodoc:
       # @private
 
-      module Wrap #:nodoc:
+      module Wrap # :nodoc:
         def initialize(_array, options)
           @line_wrap = Prawn::Text::Formatted::LineWrap.new
           @arranger = Prawn::Text::Formatted::Arranger.new(
@@ -44,7 +44,7 @@ def initialize(_array, options)
         #
         # Returns any formatted text that was not printed
         #
-        def wrap(array) #:nodoc:
+        def wrap(array) # :nodoc:
           initialize_wrap(array)
 
           stop = false
diff --git a/manual/outline/add_subsection_to.rb b/manual/outline/add_subsection_to.rb
index de6b17c54..d5f9ab93e 100644
--- a/manual/outline/add_subsection_to.rb
+++ b/manual/outline/add_subsection_to.rb
@@ -44,17 +44,17 @@
 
   outline.add_subsection_to('Section 1') do
     outline.page title: 'Added later - last position',
-                 destination: 6
+      destination: 6
   end
 
   outline.add_subsection_to('Added later - first position') do
     outline.page title: 'Another page added later',
-                 destination: 7
+      destination: 7
   end
 
   # The title provided is for a page which will be converted into a section
   outline.add_subsection_to('Page 3') do
     outline.page title: 'Last page added',
-                 destination: 8
+      destination: 8
   end
 end
diff --git a/prawn.gemspec b/prawn.gemspec
index 7c071ba16..5626666bd 100644
--- a/prawn.gemspec
+++ b/prawn.gemspec
@@ -23,7 +23,7 @@ Gem::Specification.new do |spec|
       '.yardopts'
     ]
   spec.require_path = 'lib'
-  spec.required_ruby_version = '>= 2.5'
+  spec.required_ruby_version = '>= 2.6'
   spec.required_rubygems_version = '>= 1.3.6'
 
   spec.authors = [
@@ -42,7 +42,7 @@ Gem::Specification.new do |spec|
 
   spec.add_development_dependency('pdf-inspector', '>= 1.2.1', '< 2.0.a')
   spec.add_development_dependency('pdf-reader', ['~> 1.4', '>= 1.4.1'])
-  spec.add_development_dependency('prawn-dev', '~> 0.2.0')
+  spec.add_development_dependency('prawn-dev', '~> 0.3.0')
   spec.add_development_dependency('prawn-manual_builder', '>= 0.3.0')
 
   spec.homepage = 'http://prawnpdf.org'
diff --git a/spec/prawn/graphics_spec.rb b/spec/prawn/graphics_spec.rb
index b9f34b754..64515a62c 100644
--- a/spec/prawn/graphics_spec.rb
+++ b/spec/prawn/graphics_spec.rb
@@ -186,7 +186,7 @@
     end
 
     it 'moves the pointer to the center of the ellipse after drawing' do
-      expect(curve.coords[-2..-1]).to eq([100, 100])
+      expect(curve.coords[-2..]).to eq([100, 100])
     end
   end
 
@@ -199,7 +199,7 @@
 
     it 'strokes the same path as the equivalent ellipse' do
       middle = curve.coords.length / 2
-      expect(curve.coords[0...middle]).to eq(curve.coords[middle..-1])
+      expect(curve.coords[0...middle]).to eq(curve.coords[middle..])
     end
   end
 
diff --git a/spec/prawn_manual_spec.rb b/spec/prawn_manual_spec.rb
index e4a3f15cd..57720ccd0 100644
--- a/spec/prawn_manual_spec.rb
+++ b/spec/prawn_manual_spec.rb
@@ -6,9 +6,9 @@
 MANUAL_HASH =
   case RUBY_ENGINE
   when 'ruby'
-    'de26db4fe63e024231c0a332203b41305103d877b584a2e98dbd0561bced39f2c066b5c0c96a4686e586a9deb347f099dac4c646446dadb1521a7d4a674ae6fb'
+    '1dbd5d466eb58d4d495aee6869eb839e3995fbe8607318c491786b959f490e5aab968574a2fea8c3e42ef3d54374bc903357f5cc7b5065f5fe71999830d7c995'
   when 'jruby'
-    'c002ffaf6fe4b2877bd2244735e99c04a4b28b06bc365f343411af052d491660e0d858a956a757ad15a4ed16d6808fc8d726fd683d524f5a3f7c0c8b9566b683'
+    'e23a8336dd55ca007d93eaaacb9ef6ca4d3e91d4b6ccf5e504925212907ebf3a0c7334e1a614ee5e54de800bd4500a3b2430e038bd9f75879c4a69c68589408d'
   end
 
 RSpec.describe Prawn do