Fix issue with retrieving every single id to count them (fix #81)

Author: yurykabanov

src/NilPortugues/Laravel5/JsonApi/Controller/JsonApiTrait.php

@@ -63,7 +63,7 @@ protected function totalAmountResourceCallable()
         return function () {
             $idKey = $this->getDataModel()->getKeyName();
 
-            return $this->getDataModel()->query()->get([$idKey])->count();
+            return $this->getDataModel()->query()->count([$idKey]);
         };
     }