Remove superfluous '-' in site prefix (needs to be re-added for v2015.1!)

site.conf

@@ -1,5 +1,5 @@
 {
-	hostname_prefix = 'FF-DO-',
+	hostname_prefix = 'FF-DO',
 	site_name = 'Freifunk Dortmund',
 	site_code = 'ffdo',
 	opkg_repo = 'http://openwrt.draic.info/barrier_breaker/14.07/%S/packages',