Fix missing formatting argument in ValueError message

cubicweb_jsonschema/mappers/collection.py

@@ -213,7 +213,8 @@ class CollectionItemMapper(JSONSchemaMapper):
         "title" properties.
         """
         if schema_role == CREATION_ROLE:
-            raise ValueError('{} is not appropriate for submission role')
+            raise ValueError(
+                '{} is not appropriate for submission role'.format(self))
         schema = {
             'type': 'object',
             'properties': {