Use "GitHub actions" to run CI tests for google/mobly (#736)
Use "GitHub actions" to run CI tests for google/mobly (#736)

Because Travis CI seems down and we can't get CI signal for google/mobly.     
We want to replace the "Travis CI" with "GitHub actions".
It not only can cover Linux but also Windows and MacOS with simple config files.
This PR add "GitHub actions" and delete "Travis CI" in the next PR.
google/mobly