[gnome-chess] Update copyright year

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 9bfd236a148eb2e67f594246ae1c53aa772c57a2
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Fri Dec 4 13:13:33 2020 -0600

    Update copyright year

 src/gnome-chess.vala | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/gnome-chess.vala b/src/gnome-chess.vala
index ca586e9..cb2ed83 100644
--- a/src/gnome-chess.vala
+++ b/src/gnome-chess.vala
@@ -1,7 +1,7 @@
 /* -*- Mode: vala; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
  *
  * Copyright (C) 2010-2013 Robert Ancell
- * Copyright (C) 2013-2014 Michael Catanzaro
+ * Copyright (C) 2013-2020 Michael Catanzaro
  * Copyright (C) 2015-2016 Sahil Sareen
  *
  * This program is free software: you can redistribute it and/or modify it under
@@ -72,7 +72,7 @@ public class ChessApplication : Gtk.Application
     private ChessEngine? opponent_engine = null;
     private int engine_timeout_counter = 10;
     private string copyrights = """Copyright © 2010–2013 Robert Ancell
-Copyright © 2013–2018 Michael Catanzaro
+Copyright © 2013–2020 Michael Catanzaro
 Copyright © 2015–2016 Sahil Sareen""";
 
     private const GLib.ActionEntry[] app_entries =