move from travis to github actions for release

see https://www.jeffgeerling.com/blog/2020/travis-cis-new-pricing-plan-threw-wrench-my-open-source-works

details on migration: 
- https://docs.github.com/en/actions/migrating-to-github-actions/migrating-from-travis-ci-to-github-actions
- https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-java-with-gradle