Bump rexml from 3.3.0 to 3.3.9

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.0 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@v3.3.0...v3.3.9)

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

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

Gemfile.lock

@@ -118,8 +118,7 @@ GEM
     rb-inotify (0.10.1)
       ffi (~> 1.0)
     regexp_parser (2.9.2)
-    rexml (3.3.0)
-      strscan
+    rexml (3.3.9)
     rouge (4.1.3)
     rspec (3.13.0)
       rspec-core (~> 3.13.0)
@@ -149,7 +148,6 @@ GEM
       rexml (~> 3.2, >= 3.2.5)
       rubyzip (>= 1.2.2, < 3.0)
       websocket (~> 1.0)
-    strscan (3.1.0)
     terminal-table (3.0.2)
       unicode-display_width (>= 1.1.1, < 3)
     thread_safe (0.3.6)