Minor change

SketchAssistant/SketchAssistantWPF/App.xaml

@@ -2,7 +2,8 @@
              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:local="clr-namespace:SketchAssistantWPF"
-             StartupUri="MainWindow.xaml">
+             StartupUri="MainWindow.xaml"
+             ShutdownMode="OnMainWindowClose">
     <Application.Resources>
          
     </Application.Resources>