chnage license from GPL2 to GPL3

debian/copyright

@@ -4,13 +4,13 @@ Source: https://phab.lubuntu.me/source/lubuntu-update-notifier/
 Files: *
 Copyright: © 2019 Lubuntu Team.
            © 2019 Hans P Möller <hmollercl@lubuntu.me>
-License: GPL-2+
+License: GPL-3+
 
-License: GPL-2+
+License: GPL-3+
- This program is free software; you can redistribute it and/or
+ This program is free software: you can redistribute it and/or modify
- modify it under the terms of the GNU General Public License as
+ it under the terms of the GNU General Public License as published by
- published by the Free Software Foundation; either version 2 of the
+ the Free Software Foundation, either version 3 of the License, or
- License, or (at your option) any later version.
+ (at your option) any later version.
  .
  On Debian systems, the full text of the GNU General Public License version
- 2 can be found in the file `/usr/share/common-licenses/GPL-2'.
+ 3 can be found in the file `/usr/share/common-licenses/GPL-3'.