Bump rexml from 3.3.3 to 3.3.6

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] <[email protected]>

Author: dependabot[bot]

Gemfile.lock

@@ -156,7 +156,7 @@ GEM
       rdf (~> 3.3)
       rexml (~> 3.2)
     redcarpet (3.6.0)
-    rexml (3.3.3)
+    rexml (3.3.6)
       strscan
     scanf (1.0.0)
     shacl (0.4.1)