async recognizeUtterance(utterance, model, cb) {
    const response = await this.process(
      model,
      model ? model.locale : undefined,
      utterance,
      {}
    );
    return cb(null, response);
  }
Given an utterance and the locale, returns the recognition of the utterance.
@param {String} utterance Utterance to be recognized.
@param {String} model Model of the utterance.
@param {Function} cb Callback Function.