Add "files" entry in package.json to ignore everything but listed there

[rubennorte]

That way we can save a lot of space installing the package, because right now it's including things like phantomjs.

More here: https://docs.npmjs.com/files/package.json#files

[ded]

i see. it seems as though i missed this new option in the last few months. good to know about it in the future!