Upgrade to React Native v0.23

@iamkevinlowe encountered a gnarly error #19 where babel-runtime dependencies were popping up, as well some other related errors. From some searching, @bdougie discovered that babel-runtime is not needed to be explicitly added in react native v0.23.

This release removes babel-runtime and upgrades react-native

Changelog

#21 Upgrade to react-native 0.23