PHPORM-50 Remove call to deprecated Collection::count for countDocuments

https://www.mongodb.com/docs/php-library/current/reference/method/MongoDBCollection-count/

Author: GromNaN

src/Query/Builder.php

@@ -273,7 +273,7 @@ public function toMql(): array
                     $aggregations = blank($this->aggregate['columns']) ? [] : $this->aggregate['columns'];
 
                     if (in_array('*', $aggregations) && $function == 'count') {
-                        return ['count' => [$wheres, []]];
+                        return ['countDocuments' => [$wheres, []]];
                     } elseif ($function == 'count') {
                         // Translate count into sum.
                         $group['aggregate'] = ['$sum' => 1];