Fix Relation.rewhere to work with Range values

I noticed `Relation.rewhere` wasn't working with ranges:

```ruby
Post.where(comments_count: 1..3).rewhere(comments_count: 3..5).to_sql
=> "SELECT \"posts\".* FROM \"posts\" WHERE (\"posts\".\"comments_count\" BETWEEN 1 AND 3) AND (\"posts\".\"comments_count\" BETWEEN 3 AND 5)"
```

This patch ensures the above relation produces the correct SQL:

```ruby
Post.where(comments_count: 1..3).rewhere(comments_count: 3..5).to_sql
=> "SELECT \"posts\".* FROM \"posts\" WHERE (\"posts\".\"comments_count\" BETWEEN 3 AND 5)"
```

this will rebuild the array on each call, with possibly additional cost of splatting each time. unless these need to be reused outside the method, probably better to keep then in the `when` statement.