rewrite all links to prs to k8s links

pkg/apiserver/apiserver_test.go

@@ -1943,7 +1943,7 @@ func TestCreateNotFound(t *testing.T) {
 	handler := handle(map[string]rest.Storage{
 		"simple": &SimpleRESTStorage{
 			// storage.Create can fail with not found error in theory.
-			// See https://github.com/GoogleCloudPlatform/kubernetes/pull/486#discussion_r15037092.
+			// See http://pr.k8s.io/486#discussion_r15037092.
 			errors: map[string]error{"create": apierrs.NewNotFound("simple", "id")},
 		},
 	})