LICENSE: use updated GNU copy

LICENSE: use updated GNU copy

The current LICENSE file contains some form feed (FF) characters instead
of recently popular line feed (LF) characters. Also update to the latest
address of the Free Software Foundation. Lastly center some captions, as
suggested by the official GNU LICENSE distribution[0].

Historical changes of GPL-2.0 LICENSE file are availalbe[1].

[0]: https://www.gnu.org/licenses/old-licenses/gpl-2.0.txt
[1]: https://github.com/pombredanne/gpl-history

Signed-off-by: Paul Spooren <mail@aparcar.org>