Add missing references for VectorExtensions.cs (#417)

* Fix parent rotation and movement logic

* Add missing references for VectorExtensions

Author: madvlad

Assets/HoloToolkit/Utilities/Scripts/Extensions/VectorExtensions.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License. See LICENSE in the project root for license information.
 
+using System.Collections.Generic;
+using System.Linq;
 using UnityEngine;
 
 namespace HoloToolkit.Unity