Bump xos libraries to version 4.0.0

Change-Id: I07891c1f308593cef9b0f456512630eb279cc94f
diff --git a/Makefile b/Makefile
index 866a53c..f197da5 100644
--- a/Makefile
+++ b/Makefile
@@ -60,7 +60,7 @@
 venv-service:
 	virtualenv $@;\
     source ./$@/bin/activate ; set -u ;\
-    pip install -r requirements.txt xosmigrate~=3.2.6
+    pip install -r requirements.txt xosmigrate~=4.0.0
 
 create-migration: venv-service
 	source ./venv-service/bin/activate; set -u;\