SEBA-324 reverse field numbers for manytoone relations

Change-Id: I2725a85c1c0526875864880e7d3707052dd32b98
diff --git a/Dockerfile.synchronizer b/Dockerfile.synchronizer
index a9fc894..edf0cef 100644
--- a/Dockerfile.synchronizer
+++ b/Dockerfile.synchronizer
@@ -16,7 +16,7 @@
 
 # xosproject/volt-synchronizer
 
-FROM xosproject/xos-synchronizer-base:2.1.19
+FROM xosproject/xos-synchronizer-base:2.1.21
 
 COPY xos/synchronizer /opt/xos/synchronizers/volt
 COPY VERSION /opt/xos/synchronizers/volt/