Enforce 'use strict'

As stated in the [Modules section](https://github.com/airbnb/javascript#modules), `'use strict'` needs to be declared at the top of a module

[JSHint has an option](http://www.jshint.com/docs/options/#strict) for something like this by enforcing the declaration of the statement at the top function scope.
Merge pull request #132 from vahan-hartooni/patch-2

Enforce 'use strict'