Change license to AGPLv3 exactly

Restrict license to GNU AGPLv3 instead of GNU AGPLv3 or any later version.

src/commands/balance.rs

@@ -2,8 +2,7 @@
 //
 // This program is free software: you can redistribute it and/or modify
 // it under the terms of the GNU Affero General Public License as
-// published by the Free Software Foundation, either version 3 of the
-// License, or (at your option) any later version.
+// published by the Free Software Foundation, version 3 of the License.
 //
 // This program is distributed in the hope that it will be useful,
 // but WITHOUT ANY WARRANTY; without even the implied warranty of