Use Next-generation convenience images in CI [changelog skip] (#178)
Use Next-generation convenience images in CI [changelog skip] (#178)

* Use Next-generation convenience images

https://circleci.com/docs/2.0/circleci-images/#next-generation-convenience-images

h/t @edmorley

* Revert change to Ruby 2.2 job

Since the new images don't exist for Ruby 2.2.

Co-authored-by: Ed Morley <1ff3463693b0fd96bc8b63e3a6bb3a4873686c0f@users.noreply.github.com>
heroku/hatchet,heroku/hatchet,heroku/hatchet