Bump xos libraries to version 4.0.0

Change-Id: I7cc0eed4930ba0948e07befd9c23b4a6e5503df1
diff --git a/xos/synchronizer/config.yaml b/xos/synchronizer/config.yaml
index 5b7a7bd..aec9473 100644
--- a/xos/synchronizer/config.yaml
+++ b/xos/synchronizer/config.yaml
@@ -15,7 +15,7 @@
 
 
 name: volt
-core_version: ">=3.2.8"
+core_version: ">=4.0.0"
 required_models:
   - VOLTService
   - VOLTServiceInstance