debian: Fix debian/copyright syntax

Change-Id: I819ca05440cca041f26e7800821f4763f887c08b
diff --git a/debian/copyright b/debian/copyright
index a6507bd..e2a4b2d 100644
--- a/debian/copyright
+++ b/debian/copyright
@@ -3,11 +3,11 @@
 Source: https://osmocom.org/projects/openggsn
 
 Files: *
-Copyright (C) 2002-2004 Mondru AB, Author: Jens Jakobsen <jj@openggsn.org>
-Copyright (C) 2010-2017 Harald Welte <laforge@gnumonks.org>
-Copyright (C) 2012-2016 Holger Hans Peter Freyther <zecke@selfish.org>
-Copyright (C) 2014-2016 Pablo Neira Ayuso <pablo@gnumonks.org>
-Copyright (C) 2014-2016 sysmocom - s.f.m.c. GmbH
+Copyright: 2002-2004 Mondru AB, Author: Jens Jakobsen <jj@openggsn.org>
+           2010-2017 Harald Welte <laforge@gnumonks.org>
+           2012-2016 Holger Hans Peter Freyther <zecke@selfish.org>
+           2014-2016 Pablo Neira Ayuso <pablo@gnumonks.org>
+           2014-2016 sysmocom - s.f.m.c. GmbH
 License: GPL-2
 
 Files: lib/getopt.c