Fix travis build

See http://markcampbell.me/jekyll/heroku/2013/05/18/how-to-set-up-jekyll-on-heroku.html
Merge pull request #92 from agouge/travis-3

Fix travis build

See http://markcampbell.me/jekyll/heroku/2013/05/18/how-to-set-up-jekyll-on-heroku.html and #91.