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/google.golang.org/grpc/internal/transport/flowcontrol.go

@@ -136,12 +136,10 @@ type inFlow struct {
 
 // newLimit updates the inflow window to a new value n.
 // It assumes that n is always greater than the old limit.
-func (f *inFlow) newLimit(n uint32) uint32 {
+func (f *inFlow) newLimit(n uint32) {
 	f.mu.Lock()
-	d := n - f.limit
 	f.limit = n
 	f.mu.Unlock()
-	return d
 }
 
 func (f *inFlow) maybeAdjust(n uint32) uint32 {