code: function rollback(client, done, error, callback) {
    client.query('ROLLBACK', rollbackError => {
      done(rollbackError);
      return callback(rollbackError || error, null);
    });
  }
docs: Rolls back any failed transaction.
  @param  {Client}   client
  @param  {Function} done
  @param  {Error}    error
  @param  {Function} callback
  @private