Bump rexml from 3.3.9 to 3.4.0

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.9 to 3.4.0.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.3.9...v3.4.0)

---
updated-dependencies:
- dependency-name: rexml
  dependency-type: indirect
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile.lock

@@ -45,7 +45,7 @@ GEM
     rainbow (3.1.1)
     rake (13.2.1)
     regexp_parser (2.9.3)
-    rexml (3.3.9)
+    rexml (3.4.0)
     rmagick (6.0.1)
       observer (~> 0.1)
       pkg-config (~> 1.4)