Update appdata file for license tag changes

Author: kaiw

data/meld.appdata.xml.in

@@ -1,8 +1,9 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<!-- Copyright 2013 Kai Willadsen <kai.willadsen@gmail.com> -->
+<!-- Copyright 2013-2014 Kai Willadsen <kai.willadsen@gmail.com> -->
 <application>
  <id type="desktop">meld.desktop</id>
- <licence>CC0</licence>
+ <metadata_license>CC0-1.0</metadata_license>
+ <project_license>GPL-2.0+ and CC-BY-SA-3.0</project_license>
  <description>
   <_p>
   Meld is a visual diff and merge tool targeted at developers. Meld helps you