Bump rexml from 3.3.8 to 3.3.9

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.8 to 3.3.9.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](https://github.com/ruby/rexml/compare/v3.3.8...v3.3.9)

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

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

Gemfile.lock

@@ -221,7 +221,7 @@ GEM
     regexp_parser (2.9.2)
     reline (0.5.10)
       io-console (~> 0.5)
-    rexml (3.3.8)
+    rexml (3.3.9)
     rspec-core (3.13.1)
       rspec-support (~> 3.13.0)
     rspec-expectations (3.13.3)