Add '.babelrc' to npmignore

[jluxenberg]

react-native projects use Babel 6 and the current .babelrc
in version 0.1.12 published on npm is incompatible with Babel 6.

The babelrc file for an npm module should not be in the npm
package at all, since transpilation should be done before publishing
to npm, so we add .babelrc file to the npmignore file.

See similar issue in redux-thunk for more details
reduxjs/redux-thunk#43

[raineorshine]

This should be ready to merge.

@ashaffer Let me know if you need contributor support! There are only a few issues, and I doubt this will iterate much given how small the scope is.