Bump rexml from 3.3.7 to 3.3.9

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.7 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@v3.3.7...v3.3.9)

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

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

Gemfile.lock

@@ -108,7 +108,7 @@ GEM
       pry (>= 0.13, < 0.15)
     public_suffix (5.0.5)
     rainbow (3.1.1)
-    rexml (3.3.7)
+    rexml (3.3.9)
     ruby-progressbar (1.13.0)
     thor (1.3.1)
     toml-rb (2.2.0)