ci: add `.travis.yml` for Travis CI builds
ci: add `.travis.yml` for Travis CI builds

See https://travis-ci.org/dherges/ng-packagr
DavidParks8/ng-packagr,DavidParks8/ng-packagr,dherges/ng-packagr,dherges/ng-packagr,DavidParks8/ng-packagr,DavidParks8/ng-packagr,dherges/ng-packagr,dherges/ng-packagr