Non-ES6 modules files not transpiled for jsnext:main

[chiel]

First off, thanks for this library, it's been pretty helpful to me.

I've recently switched to rollup for my bundling needs and I've run into a small issue with this package, since it does not have transpiled code for jsx syntax (and perhaps other features, did not check) which means it's unusable as jsnext:main.

I get the following error:

Error parsing ./node_modules/redux-spy/src/reduxSpy.js: Unexpected token (9:8) in ./node_modules/redux-spy/src/reduxSpy.js

Which is because rollup uses the file specified by jsnext:main field whenever present. However, it doesn't know about anything else other than es6 module syntax, so it breaks on the JSX in that file.

There is a good write-up about this stuff over at https://github.com/rollup/rollup/wiki/jsnext:main.

So the question is, are you open to fixing this, or at least open to accepting a pull request? :)