Release v2.31.0

[bquorning]

Let’s publish a plugin’ed version ✨

In the words of @koic:

AFAIK, this is the last extension gem managed by the RuboCop org that has not yet been released as a plugin. With this release, users will be able to consistently use plugins for all officially maintained gems under the RuboCop org.

Having a consistent usage pattern for gems within the RuboCop org is a meaningful step forward.

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Before submitting the PR make sure the following are checked:

• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Updated documentation.
• Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• The build (bundle exec rake) passes (be sure to run this locally, since it may produce updated documentation that you will need to commit).

[bquorning]

cc @ydah, @koic

[bquorning]

cc @pirj too

[pirj]

Fantastic! 🙌