Improve `DISTINCT ON` formatting style

input
```sql
select distinct on (col1) *
from tbl
```

actual
```sql
select
	distinct on
		(
			col1
		)
	*
from
	tbl
```

expected (by [uroboroSQL\-formatter](https://github.com/future-architect/uroboroSQL-formatter))
```sql
select
	distinct
on
	(col1)	*
from	tbl
```