deps(bundler): bump rexml from 3.3.6 to 3.3.9 (#300)

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

@@ -42,9 +42,7 @@ GEM
     public_suffix (4.0.7)
     racc (1.7.3)
     rainbow (3.1.1)
-    rexml (3.3.6)
-      strscan
-    strscan (3.1.0)
+    rexml (3.3.9)
     tomlrb (2.0.3)
     typhoeus (1.4.0)
       ethon (>= 0.9.0)