Update vendor

vendor/github.com/google/go-containerregistry/pkg/crane/digest.go

@@ -0,0 +1,40 @@
+// Copyright 2018 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 crane
+
+// Digest returns the sha256 hash of the remote image at ref.
+func Digest(ref string, opt ...Option) (string, error) {
+	o := makeOptions(opt...)
+	if o.platform != nil {
+		desc, err := getManifest(ref, opt...)
+		if err != nil {
+			return "", err
+		}
+		img, err := desc.Image()
+		if err != nil {
+			return "", err
+		}
+		digest, err := img.Digest()
+		if err != nil {
+			return "", err
+		}
+		return digest.String(), nil
+	}
+	desc, err := head(ref, opt...)
+	if err != nil {
+		return "", err
+	}
+	return desc.Digest.String(), nil
+}