Fix for CoffeeScript 1.7.x

CoffeeScript 1.7 made the following change:

*When requiring CoffeeScript files in Node you must now explicitly register the compiler. This can be done with `require 'coffee-script/register'` or `CoffeeScript.register()`. Also for configuration such as Mocha's, use `coffee-script/register`.*

Without this change, requiring mecab-ffi throws:

    Error: Cannot find module './lib/index'