vendor: update oci image spec dependency

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

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

@@ -0,0 +1,63 @@
+// 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
+
+import "github.com/opencontainers/image-spec/specs-go"
+
+// Platform describes the platform which the image in the manifest runs on.
+type Platform struct {
+	// Architecture field specifies the CPU architecture, for example
+	// `amd64` or `ppc64`.
+	Architecture string `json:"architecture"`
+
+	// OS specifies the operating system, for example `linux` or `windows`.
+	OS string `json:"os"`
+
+	// OSVersion is an optional field specifying the operating system
+	// version, for example `10.0.10586`.
+	OSVersion string `json:"os.version,omitempty"`
+
+	// OSFeatures is an optional field specifying an array of strings,
+	// each listing a required OS feature (for example on Windows `win32k`).
+	OSFeatures []string `json:"os.features,omitempty"`
+
+	// Variant is an optional field specifying a variant of the CPU, for
+	// example `ppc64le` to specify a little-endian version of a PowerPC CPU.
+	Variant string `json:"variant,omitempty"`
+
+	// Features is an optional field specifying an array of strings, each
+	// listing a required CPU feature (for example `sse4` or `aes`).
+	Features []string `json:"features,omitempty"`
+}
+
+// ManifestDescriptor describes a platform specific manifest.
+type ManifestDescriptor struct {
+	Descriptor
+
+	// Platform describes the platform which the image in the manifest runs on.
+	Platform Platform `json:"platform"`
+}
+
+// ImageIndex references manifests for various platforms.
+// This structure provides `application/vnd.oci.image.index.v1+json` mediatype when marshalled to JSON.
+type ImageIndex struct {
+	specs.Versioned
+
+	// Manifests references platform specific manifests.
+	Manifests []ManifestDescriptor `json:"manifests"`
+
+	// Annotations contains arbitrary metadata for the image index.
+	Annotations map[string]string `json:"annotations,omitempty"`
+}