Adding temp test build

__Make sure to add a https://github.com/mozilla/picl-gherkin Travis CI hook__

This PR addresses https://github.com/mozilla/picl-gherkin/issues/9 , it adds Travis CI support for picl-gherkin.
However it only tests to make sure the bundle builds properly and runs the hkdf test file.

@ckarlof mentioned that picl-gherkin will be refactored from browserify, so this is a temporary solution for the current setup.