Bump rexml from 3.3.8 to 3.3.9 in /.rundoc-workspace (#53)

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: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.rundoc-workspace/Gemfile.lock

@@ -53,7 +53,7 @@ GEM
     rack-test (2.1.0)
       rack (>= 1.3)
     regexp_parser (2.9.2)
-    rexml (3.3.8)
+    rexml (3.3.9)
     rubyzip (2.3.2)
     rundoc (3.0.0)
       aws-sdk-s3 (~> 1)