Fix frame-0023 expected output to conform with frame semantics.

Author: gkellogg

test-suite/tests/frame-0023-out.jsonld

@@ -1,8 +1,8 @@
 {
   "@context": {"ex": "http://example.org/"},
   "@graph": [{
-    "@id": "ex:Sub2",
-    "ex:p": "foo",
+    "@id": "ex:Sub1",
+    "ex:p": null,
     "ex:q": "bar"
   }]
 }