Bump rexml from 3.3.7 to 3.3.9 in /examples/ruby (SeleniumHQ#2019)

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.7 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@v3.3.7...v3.3.9)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Sri Harsha <[email protected]>
Co-authored-by: Viet Nguyen Duc <[email protected]>

Author: 3 people