don't use deprecated gtk_object_sink(), replace it with g_object_ref_sink()

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@56345 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/menu.cpp

@@ -706,7 +706,7 @@ void wxMenu::Init()
     // NB: keep reference to the menu so that it is not destroyed behind
     //     our back by GTK+ e.g. when it is removed from menubar:
     g_object_ref(m_menu);
-    gtk_object_sink(GTK_OBJECT(m_menu));
+    g_object_ref_sink(m_menu);
 
     m_owner = (GtkWidget*) NULL;