small changes I did to get this running on my machine

Hey!

I got to your project from [this](https://github.com/liabru/matter-js/issues/11) conversation on matter.js about using it with pixi. I was thinking of doing the same! I'd be curious of your results if you continue with that effort. I'm planning on doing various combinations of physics engines hooked up with graphics engines to find the right match.

Anyways I wanted to check out what the game looked like so I ran it locally and had to make some small changes to get it running, as well as building with grunt.

This pull request is merely so you can see what I did in case you want to use any pieces of it. Feel free to close it whenever. I noticed the coffee branch so no worries if you are going to completely redo everything anyways.