Bump rexml from 3.3.6 to 3.3.9

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] <support@github.com>

Gemfile.lock

@@ -38,8 +38,7 @@ GEM
     rainbow (3.0.0)
     rake (13.0.6)
     regexp_parser (2.1.1)
-    rexml (3.3.6)
-      strscan
+    rexml (3.3.9)
     rubocop (1.22.3)
       parallel (~> 1.10)
       parser (>= 3.0.0.0)
@@ -52,7 +51,6 @@ GEM
     rubocop-ast (1.13.0)
       parser (>= 3.0.1.1)
     ruby-progressbar (1.11.0)
-    strscan (3.1.0)
     unf (0.1.4)
       unf_ext
     unf_ext (0.0.8.2)