We use Ruby for CI purposes in a lot of repos (at least until T138401: Replace jsduck with JSDoc3 across all Wikimedia code bases). This means we have a small dependency chain subject to updates (and potentially security issues, as is suggested with rubocop).

Steps, not all procedural:

1. git checkout -b bump-ruby-ci
2. Edit the Gemfile and Rakefile to update to current templates, remove crud, update versions
3. bundle update
4. bundle exec rake
5. Sanity-check it still tests the right files
6. rubocop --auto-gen-config
7. Sanity-check the auto-gen'ed config is not stupid
8. bundle exec rake
9. git add Gemfile Gemfile.lock Rakefile .jsduck/
10. git commit -m "build: Update Ruby toolchain to latest"

Example: https://gerrit.wikimedia.org/r/#/c/393918/