fix wrong method in save event

Author: maxiloc

src/EloquentSubscriber.php

@@ -20,7 +20,7 @@ public function saved($model)
         /** @var \AlgoliaSearch\Index $index */
         foreach ($this->modelHelper->getIndices($model) as $index) {
             if ($this->modelHelper->indexOnly($model, $index->indexName)) {
-                $index->addObject($this->modelHelper->getAlgoliaRecord($model), $this->modelHelper->getKey($model));
+                $index->addObject($this->modelHelper->getAlgoliaRecord($model), $this->modelHelper->getObjectId($model));
             }
         }