update vendor

Signed-off-by: Roland.Ma <rolandma@yunify.com>

vendor/github.com/deislabs/oras/pkg/content/readerat.go

@@ -0,0 +1,34 @@
+package content
+
+import (
+	"io"
+
+	"github.com/containerd/containerd/content"
+)
+
+// ensure interface
+var (
+	_ content.ReaderAt = sizeReaderAt{}
+)
+
+type readAtCloser interface {
+	io.ReaderAt
+	io.Closer
+}
+
+type sizeReaderAt struct {
+	readAtCloser
+	size int64
+}
+
+func (ra sizeReaderAt) Size() int64 {
+	return ra.size
+}
+
+type nopCloser struct {
+	io.ReaderAt
+}
+
+func (nopCloser) Close() error {
+	return nil
+}