Setup repo for Travis CI

* add a travis configuration file
* update Gemfile to reflect target (github pages)
    * development dependencies are in a development group to make tests faster (not sure this worked)
* update _config.yml to ignore the vendor directory -- travis bundle installs the dependencies into the project folder under "vendor", which jekyll was trying to render as html...
Merge pull request #1 from maxjacobson/setup-travis

Setup Travis