Fix same type comparing (#261)

* Fix same type comparing

`fieldColumnType.DatabaseTypeName()` returns non capitalized string, while `fileType.SQL` returns capitalized string.
This commit aims to fix this and avoid detecting a type change when the type did not change.

* Use strings.EqualFold to compare types

migrator.go

@@ -312,7 +312,7 @@ func (m Migrator) AlterColumn(value interface{}, field string) error {
 				fileType := clause.Expr{SQL: m.DataTypeOf(field)}
 				// check for typeName and SQL name
 				isSameType := true
-				if fieldColumnType.DatabaseTypeName() != fileType.SQL {
+				if strings.EqualFold(fieldColumnType.DatabaseTypeName(), fileType.SQL) {
 					isSameType = false
 					// if different, also check for aliases
 					aliases := m.GetTypeAliases(fieldColumnType.DatabaseTypeName())