Fixes #5548 - Add gemnasium to tell us about outdated gem requirements

Gemnasium will tell us if our gems are outdated. Most importantly, it also
notifies us if there are security patches. Also, I'm removing the old Travis
badge.
Merge pull request #4034 from daviddavis/temp/20140502075435

Fixes #5548 - Add gemnasium to tell us about outdated gem requirements