Bump rexml from 3.2.8 to 3.3.6

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.8 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@v3.2.8...v3.3.6)

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

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

Gemfile.lock

@@ -140,8 +140,8 @@ GEM
  rb-inotify (0.10.1)
  ffi (~> 1.0)
  regexp_parser (2.8.2)
- rexml (3.2.8)
- strscan (>= 3.0.9)
+ rexml (3.3.6)
+ strscan
  rspec (3.12.0)
  rspec-core (~> 3.12.0)
  rspec-expectations (~> 3.12.0)