Merge pull request #2440 from MyBoon/patch-1

docs(): update doc for gesture 'on' function

js/angular/service/gesture.js

@@ -16,6 +16,7 @@ IonicModule
      * @param {function(e)} callback The function to call when the gesture
      * happens.
      * @param {element} $element The angular element to listen for the event on.
+     * @param {object} options object.
      * @returns {ionic.Gesture} The gesture object (use this to remove the gesture later on).
      */
     on: function(eventType, cb, $element, options) {