CrossAttribute is not primary model

Author: Guy Davenport

Specification/BrAPI-Schema/BrAPI-Germplasm/Cross.json

@@ -133,7 +133,7 @@
             "title": "CrossAttribute",
             "type": "object",
             "brapi-metadata": {
-                "primaryModel": true
+                "primaryModel": false
             }
         },
         "PollinationEvent": {