switch from travis to github actions

[gingerlime]

• converted from .travis.yml
• removed .travis.yml

[gingerlime]

unfortunately the rails 6.0 tests are failing, but I'm not really sure why. See https://github.com/gingerlime/clearance/actions/runs/473819643

[gingerlime]

looks like travis also fails with rails 6.0 https://travis-ci.org/github/thoughtbot/clearance/builds/753660714

[eebs]

Thank you @gingerlime this is fantastic. The last Travis run for a different PR took over 2 hours to complete, it looks like with GitHub Actions they all run collectively in under 2 minutes. 🎉

I think because it's a PR the actions are running on your fork and not showing here, but I assume once this is merged they'll appear within this repo. There was one failure but I believe this to be unrelated to this PR so I'm going to go ahead and merge this.

Thanks again for taking the time to improve Clearance!

[gingerlime]

My pleasure, @eebs 👍