Bump rexml from 3.3.4 to 3.3.9

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.4 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@v3.3.4...v3.3.9)

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

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

Author: dependabot[bot]

Diff for: Gemfile.lock

@@ -84,8 +84,7 @@ GEM
       rainbow (>= 2.0, < 4.0)
       rexml (~> 3.1)
     regexp_parser (2.9.2)
-    rexml (3.3.4)
-      strscan
+    rexml (3.3.9)
     rspec (3.13.0)
       rspec-core (~> 3.13.0)
       rspec-expectations (~> 3.13.0)
@@ -124,7 +123,6 @@ GEM
       simplecov_json_formatter (~> 0.1)
     simplecov-html (0.12.3)
     simplecov_json_formatter (0.1.4)
-    strscan (3.1.0)
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
     unicode-display_width (2.5.0)