Distribute minified version to npm #13

Now that unpkg has been battle tested, it would be awesome if you could distribute the latest version on npm, including the minified version.

This would allow us to simply check for the presence of window.EventSource and if it is not found, load https://npmcdn.com/eventsource-polyfill@0.9.7/dist/eventsource.min.js

Thanks for making this polyfill, by the way.