Summary:
This will fail CI if we forgot to run `yarn prettier` before committing.
We do the same in React repo. It prevents committing stale files that later cause unexpected changes.
Pull Request resolved: https://github.com/facebook/prepack/pull/2212
Differential Revision: D8784406
Pulled By: gaearon
fbshipit-source-id: ca948b8e088be8886c8ba865f280ba8d72750f69
