Bump rexml from 3.2.6 to 3.3.3

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.6 to 3.3.3.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.2.6...v3.3.3)

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

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile.lock

@@ -20,10 +20,12 @@ GEM
       kramdown (~> 2.0)
     minitest (5.22.3)
     prism (0.27.0)
-    rexml (3.2.6)
+    rexml (3.3.3)
+      strscan
     rouge (4.2.1)
     sirop (0.4)
       prism (~> 0.27.0)
+    strscan (3.1.0)
     tilt (2.2.0)
 
 PLATFORMS