doc: update FSF address in GPLv2 license terms

Signed-off-by: Xavier Delaruelle <[email protected]>

Author: xdelaruelle

COPYING.GPLv2

@@ -2,7 +2,7 @@
                        Version 2, June 1991
 
  Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
- 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ <https://fsf.org/>
  Everyone is permitted to copy and distribute verbatim copies
  of this license document, but changing it is not allowed.