chore(deps): 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>

Author: dependabot[bot]

Gemfile.lock

@@ -75,8 +75,7 @@ GEM
     regexp_parser (2.9.2)
     reverse_markdown (2.1.1)
       nokogiri
-    rexml (3.3.6)
-      strscan
+    rexml (3.3.9)
     rouge (4.3.0)
     rspec (3.13.0)
       rspec-core (~> 3.13.0)
@@ -120,7 +119,6 @@ GEM
       unicode-display_width (>= 1.5, < 3.0)
       unicode_utils (~> 1.4)
     strings-ansi (0.2.0)
-    strscan (3.1.0)
     thor (1.3.1)
     tty-color (0.6.0)
     tty-cursor (0.7.1)