lib/protocols/gcm.js
function Sender(options) {
  EventEmitter.call(this);
  _.extend(this, _.defaults(options || {}, {
    retries: 4
  }));
}
function Sender(options) {
  EventEmitter.call(this);
  _.extend(this, _.defaults(options || {}, {
    retries: 4
  }));
}
Create a new GCM sender.

@param {object} options
@param {string} options.apiKey
@param {number} options.retries