Version 1.5.9 of this package is not Flow clean with Flow 0.32.0

[bolinfest]

One thing that I do in Nuclide that works with Node/Flow:

import invariant from 'assert';

This introduces invariant() in scope, which Flow likes, while providing the desired runtime behavior of invariant() without having to add anything to your package.json.

[brentvatne]

Tracking in #87 -- a PR would be very welcome :)