Modernize CI setup

[markerikson]

TravisCI appears to be mostly dead for OSS projects at this point.

We should switch to Github Actions instead. Also interested in any other updates that would be beneficial, like dropping support for outdated Node versions and testing the TS typings against multiple versions of TS.

It may also be worth borrowing some setup from Redux Toolkit at this point:

https://github.com/reduxjs/redux-toolkit/blob/ba8c911c53e67365499ac00982f640b369360a64/.github/workflows/tests.yml

[markerikson]

Looks like @eXamadeus might be doing some of this already in #480 .