build(deps): Bump rexml from 3.3.4 to 3.3.6

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.4 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@v3.3.4...v3.3.6)

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

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

Gemfile.lock

@@ -25,7 +25,7 @@ GEM
       unicode-scripts (~> 1.0)
     net-http-persistent (4.0.2)
       connection_pool (~> 2.2)
-    rexml (3.3.4)
+    rexml (3.3.6)
       strscan
     strscan (3.1.0)
     unicode-blocks (1.9.0)