Update LICENSE file so it gets properly displayed

GitHub treats LICENSE files in a particular fashion. Whenever this file
is present in a repository, an icon is displayed at the top of the
repository page. This commit enables this behavior.

LICENSE text itself was updated to mirror the one from gnu.org website,
which had some differences such as https everywhere.

LICENSE

@@ -1,7 +1,7 @@
 GNU AFFERO GENERAL PUBLIC LICENSE
    Version 3, 19 November 2007
 
- Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
+Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
 Everyone is permitted to copy and distribute verbatim copies
 of this license document, but changing it is not allowed.
 
@@ -643,7 +643,7 @@ the "copyright" line and a pointer to where the full notice is found.
 GNU Affero General Public License for more details.
 
 You should have received a copy of the GNU Affero General Public License
-    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 Also add information on how to contact you by electronic and paper mail.
 
@@ -658,4 +658,4 @@ specific requirements.
 You should also get your employer (if you work as a programmer) or school,
 if any, to sign a "copyright disclaimer" for the program, if necessary.
 For more information on this, and how to apply and follow the GNU AGPL, see
-<http://www.gnu.org/licenses/>.
+<https://www.gnu.org/licenses/>.

README.md

@@ -22,7 +22,7 @@ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU Affero General Public License for more details.
 
 You should have received a copy of the GNU Affero General Public License
-along with this program.  If not, see <http://www.gnu.org/licenses/>.
+along with this program. If not, see <https://www.gnu.org/licenses/>.
 
 Want to use Snap! but scared by the open-source license? Get in touch with us,
 we'll make it work.