Summary:
1. Animation guide page is the only place where Flowtype is used, it would be better to remove it to prevent some confusion.
2. ES2015 classes in guidelines docs pages and fixed some typos
**Test plan (required)**
Should i write any tests for this?
Closes https://github.com/facebook/react-native/pull/8339
Differential Revision: D3474192
Pulled By: bestander
fbshipit-source-id: 5531d1e399eaed0952732ac2e0bd1effc72d00a8
590f90fe2e