async subscribe(event, args) {
    await this.request(RPCCommands.SUBSCRIBE, args, event);
    return {
      unsubscribe: () => this.request(RPCCommands.UNSUBSCRIBE, args, event),
    };
  }
Subscribe to an event
@param {string} event Name of event e.g. `MESSAGE_CREATE`
@param {Object} [args] Args for event e.g. `{ channel_id: '1234' }`
@returns {Promise<Object>}