Bugfix: Correct copyright year in Mac DMG background image

contrib/macdeploy/background.svg

@@ -3,7 +3,7 @@
  "http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd">
 <svg version="1.0" xmlns="http://www.w3.org/2000/svg" width="1000pt" height="640pt" viewBox="0 0 1000 640" preserveAspectRatio="xMidYMid meet">
 	<!-- kate: space-indent off;
-	Copyright (c) 2011-2013 The Bitcoin Core developers
+	Copyright (c) 2015 The Bitcoin Core developers
 	Distributed under the MIT software license, see the accompanying
 	file COPYING or http://www.opensource.org/licenses/mit-license.php.
 	-->