Updated for Ruby 2.3, added Travis CI build

[szTheory]

You can see the passing build here. Please note that the build fails for Ruby 1.9.3 and Ruby 2.4, which you can see here. The reason for Ruby 2.4 incompatibility is an issue with the current version of fakeweb. If you look at the latest Issues for fakeweb you'll see that it hasn't been updated in many years, an while the maintainer says or plans on updating it there hasn't been any movement in the past year so I wouldn't hold my breath on it.