Slim down NPM package

[avaly]

This PR slims down the NPM package by removing the docs and any additional development config files. See http://blog.npmjs.org/post/165769683050/publishing-what-you-mean-to-publish for reasoning.

$ npm pack
react-toggle-4.0.2.tgz

$ tar tvf react-toggle-4.0.2.tgz 
-rw-rw-r-- 1000/1000      2105 2017-10-15 13:01 package/package.json
-rw-rw-r-- 1000/1000      2926 2017-10-15 12:56 package/README.md
-rw-rw-r-- 1000/1000      1085 2017-10-15 12:56 package/LICENSE
-rw-rw-r-- 1000/1000       652 2017-10-15 13:01 package/dist/component/check.js
-rw-rw-r-- 1000/1000      9018 2017-10-15 13:01 package/dist/component/index.js
-rw-rw-r-- 1000/1000       722 2017-10-15 13:01 package/dist/component/util.js
-rw-rw-r-- 1000/1000       696 2017-10-15 13:01 package/dist/component/x.js
-rw-rw-r-- 1000/1000      1440 2017-10-15 12:56 package/CHANGELOG.md
-rw-rw-r-- 1000/1000      3021 2017-10-15 12:56 package/style.css

[jorrit]

I think this is still relevant. If you want the docs to stay perhaps you can minify the JS file and leave out the source map. This will already save a lot.