added commonjs package manager support

[arnochauveau]

makes it possible to use ng-cordova with your favorite commonjs package manager(componentjs, webpack, etc..):

var ngCordova = require('ng-cordova');

angular.module('my-app', [ngCordova]);

or in ES6:

import * as ngCordova from 'ng-cordova';

angular.module('my-app', [ngCordova]);