MT#58381 Use short name for GPL-3 in debian/copyright

Change-Id: Iaecf11c27d35d3d7fdddb991f2a81398727bc6a0

debian/copyright

@@ -5,7 +5,7 @@ Upstream-Name: repoapi
 Files: *
 Copyright:
  Copyright © 2015-2021 Sipwise GmbH, Austria
-License: GPL-3.0+
+License: GPL-3+
  This program is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or