Expose module through the UMD format

This change allows this module to be consumed by a variety of different
module loaders. If either Node or Component are the environment its
running in, it will expose itself via `module.exports`. If an AMD loader
is present, it will expose itself as an AMD module. In the event that no
such system is present, it will simply expose a global called
randomColor (the same as it used to always do).