Update ping pong charm

Signed-off-by: Philip Joseph <philip.joseph@riftio.com>
diff --git a/layers/pingpong/layer.yaml b/layers/pingpong/layer.yaml
index aa4dc07..833eea6 100644
--- a/layers/pingpong/layer.yaml
+++ b/layers/pingpong/layer.yaml
@@ -1,3 +1,4 @@
 includes:
     - layer:basic
     - layer:vnfproxy
+repo: https://osm.etsi.org/gerrit/osm/juju-charms