Change copyright file to point to GPL-2 instead of GPL

Warned-by: lintian

debian/changelog

@@ -16,6 +16,7 @@ dpkg (1.17.0) UNRELEASED; urgency=low
     best value, to avoid flip-flops of alternatives with equal priority.
     Closes: #699807
   * Fix clang warnings due to change of alignment requirements.
+  * Change copyright file to point to GPL-2 instead of GPL.
 
  -- Guillem Jover <guillem@debian.org>  Fri, 03 Aug 2012 13:21:00 +0200
 

debian/copyright

@@ -56,5 +56,5 @@ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.
 
 On Debian systems, the complete text of the GNU General Public License
-can be found in ‘/usr/share/common-licenses/GPL’ or in the dpkg source
+can be found in ‘/usr/share/common-licenses/GPL-2’ or in the dpkg source
 as the file ‘COPYING’.