fix migrator default value regexp (#148)

example:

"country" varchar(4) DEFAULT 'CN'

column.DefaultValueValue = "'CN'::character varying"

migrator.go

@@ -423,7 +423,7 @@ func (m Migrator) ColumnTypes(value interface{}) (columnTypes []gorm.ColumnType,
 			}
 
 			if column.DefaultValueValue.Valid {
-				column.DefaultValueValue.String = regexp.MustCompile(`'(.*)'::[\w]+$`).ReplaceAllString(column.DefaultValueValue.String, "$1")
+				column.DefaultValueValue.String = regexp.MustCompile(`'(.*)'::[\w\s]+$`).ReplaceAllString(column.DefaultValueValue.String, "$1")
 			}
 
 			if datetimePrecision.Valid {