Website: Does not show neutral quaternary colors

The `neutralQuaternary` and `neutralQuaternaryAlt` colors are missing from the [colors page](https://developer.microsoft.com/en-us/fabric#/styles/colors) on the website: 
![image](https://user-images.githubusercontent.com/1382445/36510156-fa4fd38e-1716-11e8-9d32-399930c3cec8.png)
