[gtkmm/gtkmm-3-24] gtk/gtkmm.h: Update the link to libsigc++'s home page

[Kjell Ahlstedt <kjellahl src gnome org>]

commit b8a056b9a2a49906421223fced794259f2ff64c1
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Tue Oct 6 12:59:34 2020 +0200

    gtk/gtkmm.h: Update the link to libsigc++'s home page

 gtk/gtkmm.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gtk/gtkmm.h b/gtk/gtkmm.h
index bc8dca75..59b41422 100644
--- a/gtk/gtkmm.h
+++ b/gtk/gtkmm.h
@@ -42,7 +42,7 @@
  *   <a href="http://www.gtk.org/";>the GTK+ website</a> for more information.
  * - Use inheritance to derive custom widgets.
  * - Type-safe signal handlers (slots), in standard C++, using
- *   <a href="http://libsigc.sourceforge.net/";>libsigc++</a>.
+ *   <a href="https://libsigcplusplus.github.io/libsigcplusplus/";>libsigc++</a>.
  * - Polymorphism.
  * - Use of the Standard C++ Library, including strings, containers and
  *   iterators.