Do not deploy when GIT_NAME is not defined.

This should stop deployment when Travis is run on forks.
In plain English (so I won't get tripped up by Ruby stuff):

Current behavior: "if the environment variable TRAVIS_PULL_REQUEST is set, do not deploy and output a message to that effect."

New additional behavior: "if the environment variable GIT_NAME is NOT set, do not deploy and output a message to the effect that we won't deploy on a fork"

I dont seem to be able to translate a simple statement like that into Ruby correctly :-(