Node.js `require('colors.css')` should return `colors` from `js/colors.js`

Currently the code `require('colors.css')` is meaningless in Node.js and similar environments (such as [Browserify](http://browserify.org/) or [node-webkit](https://github.com/rogerwang/node-webkit/)) though they might utilize the npm package `colors.css`.

This pull request detects Node.js [`module.exports`](http://nodejs.org/docs/latest/api/modules.html#modules_module_exports) and uses it to return the `colors` object from `js/colors.js` whenever the code `require('colors.css')` is used.