Bump rexml from 3.2.6 to 3.3.6

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.6 to 3.3.6.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.2.6...v3.3.6)

---
updated-dependencies:
- dependency-name: rexml
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile.lock

@@ -421,7 +421,8 @@ GEM
     responders (3.1.1)
       actionpack (>= 5.2)
       railties (>= 5.2)
-    rexml (3.2.6)
+    rexml (3.3.6)
+      strscan
     rollbar (3.5.2)
     rouge (4.2.1)
     rspec-collection_matchers (1.2.1)
@@ -499,6 +500,7 @@ GEM
       actionpack (>= 5.2)
       activesupport (>= 5.2)
       sprockets (>= 3.0.0)
+    strscan (3.1.0)
     terminal-table (3.0.2)
       unicode-display_width (>= 1.1.1, < 3)
     text (1.3.1)