Keep gh-pages and master in sync with one line of code

If you publish projects to Github, then you may be using a [gh-pages branch](https://help.github.com/articles/creating-project-pages-manually/) to create a nice home for your project with a demo and some documentation. A common pattern is to keep the gh-pages and master branches in sync with each other — whatever code is in master is the same as your project page (gh-pages).