Bump rexml from 3.3.3 to 3.3.6

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.3 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@v3.3.3...v3.3.6)

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

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

Gemfile.lock

@@ -103,7 +103,7 @@ GEM
     rainbow (3.1.1)
     rake (13.0.6)
     regexp_parser (2.6.0)
-    rexml (3.3.3)
+    rexml (3.3.6)
       strscan
     rspec (3.11.0)
       rspec-core (~> 3.11.0)