Summary:
Attempt to fix https://github.com/facebook/react-native/pull/8612
We re-named `mainActivityPath` by `mainFilePath` in the `link` code, but we forgot to rename config parameters. Currently, link is broken.
- [x] `react-native link` should work for react-native 0.29+
Closes https://github.com/facebook/react-native/pull/8807
Differential Revision: D3576176
fbshipit-source-id: 60ecbd660563923696bbef1ed3b0900a7d58469f