Summary: `'invariant'` can only be resolved by chance if node modules have been installed with npm3 or yarn, as it is a transitive dependency of `babel-traverse`. This changes the import to the direct dependency `fbjs/lib/invariant`.
Reviewed By: jeanlauliac, astreet
Differential Revision: D4462471
fbshipit-source-id: 5c841845012ed22a7c6264d46326a47807948513