message: close returns promise like in AudioContext
diff: @@ -81,10 +81,11 @@ define(["Tone/core/Tone", "Tone/core/Context"], function (Tone) {
  /**
  * Close the context
  - * @return {Number}
  + * @return {Promise}
  */
  Tone.OfflineContext.prototype.close = function(){
  this._context = null;
  + return Promise.resolve();
  };
  return Tone.OfflineContext;
  