travis ci config

configured travis-ci for the plugin

Testing Done:
https://travis-ci.org/pantsbuild/intellij-pants-plugin/builds/42278896

Reviewed at https://rbcommons.com/s/twitter/r/1408/
support excluded source roots

Testing Done:
an added integration tests is passing now

Reviewed at https://rbcommons.com/s/twitter/r/1411/