[gtk/clipboard-demo-fixes] gtk-demo: Update copyright year

[Matthias Clasen <matthiasc src gnome org>]

commit f645c063fb7780442c8c7e14b68fecdc60ecfa0a
Author: Matthias Clasen <mclasen redhat com>
Date:   Sun Apr 26 00:44:48 2020 -0400

    gtk-demo: Update copyright year

 demos/gtk-demo/main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/demos/gtk-demo/main.c b/demos/gtk-demo/main.c
index f61f4bac62..37f0901ea1 100644
--- a/demos/gtk-demo/main.c
+++ b/demos/gtk-demo/main.c
@@ -70,7 +70,7 @@ activate_about (GSimpleAction *action,
   gtk_show_about_dialog (GTK_WINDOW (gtk_application_get_active_window (app)),
                          "program-name", "GTK Demo",
                          "version", version,
-                         "copyright", "© 1997—2019 The GTK Team",
+                         "copyright", "© 1997—2020 The GTK Team",
                          "license-type", GTK_LICENSE_LGPL_2_1,
                          "website", "http://www.gtk.org";,
                          "comments", "Program to demonstrate GTK widgets",