Incorrect ColumnType Nullable default

[ChrisPortman]

Description

Sqlite coumns that are neither NOT NULL or NULL are nullable by default. However, .Nullable() defaults to false and is only set true if the CREATE TABLE sql explicitly denotes the column as NULL

https://github.com/go-gorm/sqlite/blob/397ec6fa8c64060db1dd392675cf51ab919c4c3c/ddlmod.go#L122

columnType := migrator.ColumnType{
    <snip>
    NullableValue:     sql.NullBool{Valid: true},    //<--- .Bool implicitly false, i.e. NOT NULL 
    <snip>
}

matchUpper := strings.ToUpper(matches[3])
if strings.Contains(matchUpper, " NOT NULL") {
	columnType.NullableValue = sql.NullBool{Bool: false, Valid: true}
} else if strings.Contains(matchUpper, " NULL") {
	columnType.NullableValue = sql.NullBool{Bool: true, Valid: true}
}
...

[ChrisPortman]

I think this is also raised by #107