Use the getAttributes method on insert (laravel#25349)

Update the performInsert method to use getAttributes instead of accessing the property directly.

src/Illuminate/Database/Eloquent/Model.php

@@ -681,7 +681,7 @@ protected function performInsert(Builder $query)
         // If the model has an incrementing key, we can use the "insertGetId" method on
         // the query builder, which will give us back the final inserted ID for this
         // table from the database. Not all tables have to be incrementing though.
-        $attributes = $this->attributes;
+        $attributes = $this->getAttributes();
 
         if ($this->getIncrementing()) {
             $this->insertAndSetId($query, $attributes);