vendor: include github.com/opencontainers/image-spec

Signed-off-by: Stephen J Day <stephen.day@docker.com>

vendor/github.com/opencontainers/image-spec/specs-go/v1/descriptor.go

@@ -0,0 +1,30 @@
+// Copyright 2016 The Linux Foundation
+//
+// 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 v1
+
+// Descriptor describes the disposition of targeted content.
+type Descriptor struct {
+	// MediaType contains the MIME type of the referenced object.
+	MediaType string `json:"mediaType"`
+
+	// Digest is the digest of the targeted content.
+	Digest string `json:"digest"`
+
+	// Size specifies the size in bytes of the blob.
+	Size int64 `json:"size"`
+
+	// URLs specifies a list of URLs from which this object MAY be downloaded
+	URLs []string `json:"urls,omitempty"`
+}