Fix namespace.

src/Avalonia.X11/X11Platform.cs

@@ -3,7 +3,7 @@ using System.Collections.Generic;
 using System.Reflection;
 using Avalonia.Controls;
 using Avalonia.Controls.Platform;
-using Avalonia.FreeDesktop.Dbus;
+using Avalonia.FreeDesktop;
 using Avalonia.Input;
 using Avalonia.Input.Platform;
 using Avalonia.OpenGL;