test case for #limit added - picking latest value from limit

Test case added for the case specified in documentation of `ActiveRecord#limit` where `limit` picks the value from latest `limit` applied to the relation.

for e.g.

```ruby
Topic.limit(2).limit(1).to_sql => "SELECT  \"players\".* FROM \"players\"  LIMIT 1"
```

Hence picking up the latest value supplied in `limit`