Update go dependencies (#4524)

vendor/k8s.io/kube-openapi/pkg/util/sets/empty.go

@@ -0,0 +1,27 @@
+/*
+Copyright The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Code generated by set-gen. DO NOT EDIT.
+
+// NOTE: This file is copied from k8s.io/kubernetes/vendor/k8s.io/apimachinery/pkg/util/sets/empty.go
+// because in Kubernetes we don't allowed vendor code to import staging code. See
+// https://github.com/kubernetes/kube-openapi/pull/90 for more details.
+
+package sets
+
+// Empty is public since it is used by some internal API objects for conversions between external
+// string arrays and internal sets, and conversion logic requires public types today.
+type Empty struct{}