Bump rexml from 3.2.6 to 3.2.8

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.6 to 3.2.8.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.2.6...v3.2.8)

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

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

Gemfile.lock

@@ -291,7 +291,8 @@ GEM
       trailblazer-option (>= 0.1.1, < 0.2.0)
       uber (< 0.2.0)
     retriable (3.1.2)
-    rexml (3.2.6)
+    rexml (3.2.8)
+      strscan (>= 3.0.9)
     rouge (2.0.7)
     ruby-macho (2.5.1)
     ruby2_keywords (0.0.5)
@@ -312,6 +313,7 @@ GEM
       naturally
     sqlite3 (1.7.3)
       mini_portile2 (~> 2.8.0)
+    strscan (3.1.0)
     terminal-notifier (2.0.0)
     terminal-table (3.0.2)
       unicode-display_width (>= 1.1.1, < 3)