updates npm test script to use v1.7 of coffeescript compiler

The DevDependencies in package.json don't specify a version for coffee-script so if you npm install today (or update installed modules) coffee-script 1.7 will be installed. This requires using a slightly different compiler value for mocha (see: http://visionmedia.github.io/mocha/#compilers-option) or the tests will not run.