[gtkmm] C++11: Stack: Use of override keyword.

[Murray Cumming <murrayc src gnome org>]

commit 6a3bc909400a7d7e97cd42a00f45f556a32de0c5
Author: Murray Cumming <murrayc murrayc com>
Date:   Tue Oct 27 09:07:52 2015 +0100

    C++11: Stack: Use of override keyword.

 gtk/src/stack.hg |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gtk/src/stack.hg b/gtk/src/stack.hg
index 6dc7cb7..fd6fe4e 100644
--- a/gtk/src/stack.hg
+++ b/gtk/src/stack.hg
@@ -57,7 +57,7 @@ public:
    *
    * @deprecated Use one of the other add() methods instead. This method was added only to avoid a 
compilation error.
    */
-  void add(Widget& child);
+  void add(Widget& child) override;
 
   _WRAP_METHOD(void set_visible_child(Widget& child), gtk_stack_set_visible_child)