Update containerd to v1.2.8

Signed-off-by: Jintao Zhang <zhangjintao9020@gmail.com>

hack/dockerfile/install/containerd.installer

@@ -4,7 +4,7 @@
 # containerd is also pinned in vendor.conf. When updating the binary
 # version you may also need to update the vendor version to pick up bug
 # fixes or new APIs.
-CONTAINERD_COMMIT=85f6aa58b8a3170aec9824568f7a31832878b603 # v1.2.7
+CONTAINERD_COMMIT=a4bc1d432a2c33aa2eed37f338dceabb93641310 # v1.2.8
 
 install_containerd() {
 	echo "Install containerd version $CONTAINERD_COMMIT"