Update github.com/containerd/containerd

$ go get -u github.ccom/containerd/containerd
$ make vendor

... to silence warnings about https://github.com/advisories/GHSA-crp2-qrr5-8pq7 ,
in code we don't use.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

vendor/golang.org/x/net/http2/writesched.go

@@ -32,7 +32,8 @@ type WriteScheduler interface {
 
 	// Pop dequeues the next frame to write. Returns false if no frames can
 	// be written. Frames with a given wr.StreamID() are Pop'd in the same
-	// order they are Push'd. No frames should be discarded except by CloseStream.
+	// order they are Push'd, except RST_STREAM frames. No frames should be
+	// discarded except by CloseStream.
 	Pop() (wr FrameWriteRequest, ok bool)
 }
 
@@ -52,6 +53,7 @@ type FrameWriteRequest struct {
 
 	// stream is the stream on which this frame will be written.
 	// nil for non-stream frames like PING and SETTINGS.
+	// nil for RST_STREAM streams, which use the StreamError.StreamID field instead.
 	stream *stream
 
 	// done, if non-nil, must be a buffered channel with space for