Update to a hopefully more future proof FSF address

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/cmd.c b/cmd.c
index 1dc5dbd..f3f4385 100644
--- a/cmd.c
+++ b/cmd.c
@@ -12,8 +12,7 @@
  * 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 the Free Software Foundation,
- * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
  */
 
 #include <stdio.h>