Summary:
Rename ```StyleAspectRatio``` to ```AspectRatio``` to be consistent with the other getters and setters.
Closes https://github.com/facebook/yoga/pull/512
Reviewed By: emilsjolander
Differential Revision: D4914236
Pulled By: splhack
fbshipit-source-id: 7b9ebdbf8945c4a8570c61de16d71c8d9d96bf9f