Encode latex, so hubot makes a "clean" link

## What is used to look like:
![screen shot 2014-12-29 at 3 22 07 pm](https://cloud.githubusercontent.com/assets/372235/5574236/b713197e-8f6e-11e4-9e7e-2fafeabb4abd.png)

## What it looks like now:
![screen shot 2014-12-29 at 3 22 16 pm](https://cloud.githubusercontent.com/assets/372235/5574240/be1c60d6-8f6e-11e4-8fed-897ddcfaa124.png)

## And, it still generates valid images
![image](https://cloud.githubusercontent.com/assets/372235/5574253/ef93594e-8f6e-11e4-93fc-a0863ea2b01c.png)