Update FSF address

Free Software Foundation moved to a different address.

The new address is:
51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

Sources:
  * http://www.gnu.org/licenses/lgpl-2.1
  * http://www.fsf.org/about/contact/

The commits are splitted with top-level files/directories (e.g.: Gemfile, lib/, test/).