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](ruby/rexml@v3.3.8...v3.3.9)

---
updated-dependencies:
- dependency-name: rexml
  dependency-type: direct:production
...

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

Gemfile.lock

@@ -672,7 +672,7 @@ GEM
       faraday-net_http (< 4.0.0)
       hashie (>= 1.2.0, < 6.0)
       jwt (>= 1.5.6)
-    rexml (3.3.8)
+    rexml (3.3.9)
     roar (1.2.0)
       representable (~> 3.1)
     roar-rails (1.2.0)