Minor fix

chain `values` method in `map` function (#66)

In 
```php
    collect($results['hits']['hits'])->map(function ($hit) use ($model, $models) {
            return isset($models[$hit['_id']]) ? $models[$hit['_id']] : null;
        })->filter();
```
would generate some holds which would cause `paginate` results objects rather than list.