Update copyright in files which were missing in the previous update

modules/modpython/codegen.pl

@@ -27,7 +27,7 @@ open my $out, ">", $ARGV[1] or die;
 
 print $out <<'EOF';
 /*
- * Copyright (C) 2004-2016 ZNC, see the NOTICE file for details.
+ * Copyright (C) 2004-2020 ZNC, see the NOTICE file for details.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.