migrate from TravisCI to GitHub Actions

[sullis]

Background

https://arstechnica.com/information-technology/2021/09/travis-ci-flaw-exposed-secrets-for-thousands-of-open-source-projects/

[henri-tremblay]

It looks bad indeed. I do not use any secret at travis. So EasyMock should be safe on that front.

If you are willing to do a PR for build actions, I'm in.