code: func (m *Migrate) RollbackMigration(mig *Migration) error {
  	if mig.Rollback == nil {
  		return ErrRollbackImpossible
  	}
  
  	if err := mig.Rollback(m.db); err != nil {
  		return err
  	}
  
  	sql := fmt.Sprintf("DELETE FROM %s WHERE %s = ?", m.options.TableName, m.options.IDColumnName)
  	if _, err := m.db.Exec(sql, mig.ID); err != nil {
  		return err
  	}
  	return nil
  }
docs: // RollbackMigration undo a migration.