Update copyright years on COPYRIGHT and license template

COPYRIGHT

-Copyright 2008-2020 Debexpo's contributors (see AUTHORS)
+Copyright 2008-2021 Debexpo's contributors (see AUTHORS)
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

docs/templates/new.py

@@ -3,7 +3,7 @@
 #   This file is part of debexpo
 #   https://salsa.debian.org/mentors.debian.net-team/debexpo
 #
-#   Copyright © 2020 Baptiste Beauplat <lyknode@cilg.org>
+#   Copyright © 2021 Baptiste Beauplat <lyknode@cilg.org>
 #
 #   Permission is hereby granted, free of charge, to any person
 #   obtaining a copy of this software and associated documentation