Summary:
The `flipper` dependency is being deprecated for plugins, so upgraded the plugin to new APIs. This should be pretty safe, however, I'm not sure how to test it :)
Also removed react-diff-viewer dependency, as that seemed unused.
Reviewed By: passy
Differential Revision: D28091469
fbshipit-source-id: b9be007e3fc7b0689b1e1f711849ed82a6e01716