SEBA-324 reverse field numbers for manytoone relations

Change-Id: I1850fb8fba2d95db8219f7cf7786771be724c3f3
diff --git a/Dockerfile.synchronizer b/Dockerfile.synchronizer
index 6c06124..d5f4457 100644
--- a/Dockerfile.synchronizer
+++ b/Dockerfile.synchronizer
@@ -14,7 +14,7 @@
 
 # xosproject/openstack-synchronizer
 
-FROM xosproject/xos-synchronizer-base:2.1.18
+FROM xosproject/xos-synchronizer-base:2.1.21
 
 COPY xos/synchronizer /opt/xos/synchronizers/openstack
 COPY VERSION /opt/xos/synchronizers/openstack/