Bump rexml from 3.2.8 to 3.3.6

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.8 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@v3.2.8...v3.3.6)

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

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile.lock

@@ -36,8 +36,8 @@ GEM
     racc (1.7.3)
     rainbow (3.1.1)
     regexp_parser (2.8.3)
-    rexml (3.2.8)
-      strscan (>= 3.0.9)
+    rexml (3.3.6)
+      strscan
     rspec (3.10.0)
       rspec-core (~> 3.10.0)
       rspec-expectations (~> 3.10.0)