Creates unnecessary parens

Although they shouldn't damage the logic, the extra parens sure are ugly.

If people find this project useful, it might be worth looking in to this.

Example from the tests:

```
to_blacklist.where_sql.must_equal(
  "WHERE (((((artist_mentions_count > 0)"\
  " OR (competition_rank > 7)))"\
  " OR (subjective_dislike_rating > 3)))")
```
