Doc - referencing wrong object name.
On [TextStyles](http://airbnb.io/react-sketchapp/docs/API.html#textstyles) section, there's a typo on example.

<img width="844" alt="screenshot 2017-09-26 21 55 40" src="https://user-images.githubusercontent.com/32319933/30896451-b1aa1502-a305-11e7-9ecc-a03bb9d5e42a.png">
