update preffix, in order to avoid pkg conflicts on pool
diff --git a/aptly/server/mirror/debian/cassandra.yml b/aptly/server/mirror/debian/cassandra.yml
index 3659536..3d32e6a 100644
--- a/aptly/server/mirror/debian/cassandra.yml
+++ b/aptly/server/mirror/debian/cassandra.yml
@@ -14,5 +14,5 @@
           publisher:
             component: extra
             distributions:
-              - nightly/trusty
-              - nightly/xenial
+              - trusty/nightly
+              - xenial/nightly