code: function invokeToneAsync(assistantPayload, toneAnalyzer) {
    return new Promise(function(resolve, reject) {
      toneAnalyzer.tone({ text: assistantPayload.input.text }, function(error, data) {
        if (error) {
          reject(error);
        } else {
          resolve(data);
        }
      });
    });
  }
docs: invokeToneAsync is an asynchronous function that calls the Tone Analyzer service and returns a Promise
  @param assistantPayload json object returned by the Watson Assistant Service
  @param toneAnalyzer an instance of the Watson Tone Analyzer service
  @return a Promise for the result of calling the toneAnalyzer with the assistantPayload
  (which contains the user's input text)