(1.3) Fix ReactMount import for React 15.4 (#430)
(1.3) Fix ReactMount import for React 15.4 (#430)

* Fix ReactMount import for React 15.4

Keep supporting pre-15.4 by using a try-catch and adding the correct
import statement based on whether importing it from react-dom (the new
way) fails.

gaearon/react-hot-loader,gaearon/react-hot-loader