Why:
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Dependabot issued a warning about a development dependency security
update for the [rexml] gem used by rubocop.
[rexml]: https://github.com/advisories/GHSA-8cr8-4vfw-mr7h
This Commit:
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- Ran `bundle update rexml` on the root path to update `rexml` from
3.2.4 => 3.2.5
- Updated static Gemfiles to reflect the same version
This adds Ruby 3 and Rails 6.1 to the test matrix. It also bumps all the
dev dependencies listed in the Gemfiles to the latest versions.
We may end up switching over to GitHub actions, but this should get us
covered in the meantime.