Firefox support - use unprefixed rule in demo

Demo page doesn't work in Firefox.  See screenshot below.  By removing `-webkit-` from the scss file, it works in both Chrome and Firefox.

![screen shot 2013-07-03 at 9 28 05 am](https://f.cloud.github.com/assets/95570/743672/d06f1d52-e3ec-11e2-8628-d2ce996e8f9b.png)