Merge pull request #498 from donandren/canvassmallbug

canvas attached properties arrange improvement

src/Perspex.Controls/Canvas.cs

@@ -226,7 +226,7 @@ namespace Perspex.Controls
         private static void AffectsCanvasArrangeInvalidate(PerspexPropertyChangedEventArgs e)
         {
             var control = e.Sender as IControl;
-            var canvas = control?.Parent as Canvas;
+            var canvas = control?.VisualParent as Canvas;
             canvas?.InvalidateArrange();
         }
     }