React-native and tree shaking

[rdy]

Hi,

I've been doing some experiments with tree shaking and I found one problem with the way that react-native was being imported in one of the modules in this project. I created a PR which adjusts the import slightly to be compatible with modern tree shakers. Its a very simple change, just importing the only used part of react-native instead of the whole exported object.

Would you be willing to take the commit, please check out #83