Get tests running against modern Ruby/Rails versions

[bkeepers]

👋 Thanks for the awesome project. I'm working on a project that makes extensive use of CMS, and I'm hoping to contribute a lot of updates and improvements. But first, I just wanted to get the test running against the latest version of Ruby/Rails, and these were the minimum changes needed to make this happen.

• Use GitHub Actions to run the tests (Travis CI doesn't seem to be working any more for this project, and Actions are awesome)
• Run tests against all supported versions of Ruby (2.6, 2.7, 3.0) and Rails (6.0, 6.1, but I couldn't get tests to run against 5.2)
• A few minor changes to get tests passing with Ruby 3.0 and Rails 6.1

I'd be happy to submit these as separate PRs if you'd prefer.

[bkeepers]

I think GitHub Actions won't run on this repo until there is a workflow in master, but you can see the tests running and passing in my fork here: https://github.com/sailplan/comfortable-mexican-sofa/pull/2

[shohey1226]

Any plan to merge this? At least, #942 needs to be merged in order to run on ruby3..

[bkeepers]

@GBH Any chance you could review this or consider adding me as a contributor on this repository? I have a backlog of improvements I'd like to contribute, but I'm not eager to spend the time extracting them from my app unless there's a chance they'll get merged.