update gpl mailing address

[knight-of-ni]

fixes #109

As a reminder to myself, this is what I ran to generate this pr:

find ./ -type f | xargs sed -i  's/675 Mass Ave, Cambridge, MA 02139, USA/51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA/g'
find ./ -type f | xargs sed -i  's/59 Temple Place, Suite 330, Boston, MA  02111-1307  USA/51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA/g'
find ./ -type f | xargs sed -i  's/59 Temple Place, Suite 330, Boston, MA/51 Franklin Street, Fifth Floor, Boston, MA/g'
find ./ -type f | xargs sed -i  's/02111-1307 USA/02110-1301 USA/g'

Note that I am pushing this to the branch-netatalk-3-1 branch. I can change it if that is not the right branch.

[hat001]

The contents of the COPYING file should be replaced by the following document.
https://www.gnu.org/licenses/old-licenses/gpl-2.0.txt

[knight-of-ni]

Done.

@hat001 I'm trying to get some movement on rhbz#1520024.

[slowfranklin]

Pushed to master. Thanks!