Bump rexml from 3.3.6 to 3.3.9 (#349)

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

Gemfile.lock

@@ -124,8 +124,7 @@ GEM
     regexp_parser (2.9.0)
     reline (0.4.3)
       io-console (~> 0.5)
-    rexml (3.3.6)
-      strscan
+    rexml (3.3.9)
     rspec (3.13.0)
       rspec-core (~> 3.13.0)
       rspec-expectations (~> 3.13.0)
@@ -158,7 +157,6 @@ GEM
     sqlite3 (1.7.2-x86_64-darwin)
     sqlite3 (1.7.2-x86_64-linux)
     stringio (3.1.0)
-    strscan (3.1.0)
     thor (1.3.1)
     timecop (0.9.8)
     timeout (0.4.1)