Add missing namespace

Author: jenssegers

src/Jenssegers/Eloquent/Model.php

@@ -1,6 +1,7 @@
 <?php namespace Jenssegers\Eloquent;
 
 use Jenssegers\Mongodb\Eloquent\HybridRelations;
+use Jenssegers\Mongodb\Query\Builder as QueryBuilder;
 
 abstract class Model extends \Illuminate\Database\Eloquent\Model {