Update: missed to call DDLSpec in Down migration

Signed-off-by: Gnanakeethan Balasubramaniam <gnanakeethan@gmail.com>

migration/migration.go

@@ -99,6 +99,7 @@ func (m *Migration) Up() {
 
 // Down implement in the Inheritance struct for down
 func (m *Migration) Down() {
+	m.DDLSpec()
 	switch m.ModifyType {
 	case "alter":
 		m.ModifyType = "reverse"