Summary:
Plugins can not require files outside their folder, to make sure they don't pull in any dependencies from Flipper which are not exported by the main app.
However, those imports simply resolve to `undefined`. This diff adds a check in the babel-transform for plugins and throws an error if something from outside the plugin is required.
Reviewed By: passy
Differential Revision: D10297980
fbshipit-source-id: 1606f3211103281f9f4aa7bb2f3ca4d085d0ea1b
