Bump rexml from 3.3.6 to 3.3.9 (#77)

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.6 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@v3.3.6...v3.3.9)

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

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

Gemfile.lock

@@ -219,8 +219,7 @@ GEM
     regexp_parser (2.7.0)
     reline (0.3.3)
       io-console (~> 0.5)
-    rexml (3.3.6)
-      strscan
+    rexml (3.3.9)
     rspec-core (3.12.2)
       rspec-support (~> 3.12.0)
     rspec-expectations (3.12.3)
@@ -264,7 +263,6 @@ GEM
     simplecov-html (0.12.3)
     simplecov_json_formatter (0.1.4)
     spring (4.1.1)
-    strscan (3.1.0)
     thor (1.3.1)
     timeout (0.4.1)
     tzinfo (2.0.6)