Fix ref to namespace of Debounce extention

Author: Rosuavio

Microsoft.Toolkit.Uwp.SampleApp/SamplePages/CanvasPathGeometry/CanvasPathGeometryPage.xaml.cs

@@ -8,7 +8,7 @@
 using System.Text;
 using Microsoft.Graphics.Canvas.Geometry;
 using Microsoft.Graphics.Canvas.UI.Xaml;
-using Microsoft.Toolkit.Uwp.UI.Extensions;
+using Microsoft.Toolkit.Uwp.Extensions;
 using Microsoft.Toolkit.Uwp.UI.Media.Geometry;
 using Windows.System;
 using Windows.UI;