Update vendor

vendor/github.com/google/go-containerregistry/pkg/legacy/doc.go

@@ -0,0 +1,18 @@
+// Copyright 2019 Google LLC All Rights Reserved.
+//
+// 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.
+
+// Package legacy provides functionality to work with docker images in the v1
+// format.
+// See: https://github.com/moby/moby/blob/master/image/spec/v1.md
+package legacy