chain values method in map function (ErickTamayo#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.

Author: xcaptain

src/ElasticsearchEngine.php

@@ -203,7 +203,7 @@ public function map($results, $model)
 
         return collect($results['hits']['hits'])->map(function ($hit) use ($model, $models) {
             return isset($models[$hit['_id']]) ? $models[$hit['_id']] : null;
-        })->filter();
+        })->filter()->values();
     }
 
     /**