Bump rexml from 3.3.3 to 3.3.6 in /dev-app (#794)

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.3 to 3.3.6.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.3.3...v3.3.6)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

dev-app/Gemfile.lock

@@ -75,7 +75,7 @@ GEM
     netrc (0.11.0)
     nkf (0.2.0)
     public_suffix (4.0.7)
-    rexml (3.3.3)
+    rexml (3.3.6)
       strscan
     ruby-macho (2.5.1)
     strscan (3.1.0)