Update GPL-2 license grant.

Avoid outdated FSF postal address.

util/wmmenugen_parse_wmconfig.c

@@ -16,8 +16,7 @@
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License along
- * with this program; if not, write to the Free Software Foundation, Inc.,
- * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ * with this program; if not, see <https://www.gnu.org/licenses/>.
  */
 
 #include <sys/types.h>