If you use the current default version (CDN-powered) or if you use a local copy of reveal.js library (see [1]), you will need to serve the current directory to get the slideshow working properly.
For reference, here you have one way to custom config your slides to render ok using a local copy of reveal.js: 
[1] http://nbviewer.ipython.org/urls/gist.github.com/damianavila/5970218/raw/766d41eab9a16850a2a4447f14e93e7ed88f6b08/using_local_reveal.ipynb