Change default target platform for maven build to galileo

Starting with 0.9 we do no longer support ganymede.
http://dev.eclipse.org/mhonarc/lists/egit-dev/msg01277.html

Change-Id: Ibf40342f67d9706e86336748f15d10ea47278096
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.packaging/pom.xml

@@ -60,7 +60,7 @@
 
   <properties>
     <tycho-version>0.8.0</tycho-version>
-    <eclipse-site>http://download.eclipse.org/releases/ganymede</eclipse-site>
+    <eclipse-site>http://download.eclipse.org/releases/galileo</eclipse-site>
   </properties>
 
   <modules>