Move release flow from travis to github actions

Following [this](https://github.com/testing-library/dom-testing-library/pull/809#issue-515554670) PR by @kentcdodds, we're migrating all travis pipelines to github actions :)

An example for the action can be seen [here](https://github.com/testing-library/dom-testing-library/blob/master/.github/workflows/validate.yml).