vendor: update zfs dependency

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

vendor.conf

@@ -76,7 +76,7 @@ k8s.io/kubernetes v1.10.0-rc.1
 k8s.io/utils 258e2a2fa64568210fbd6267cf1d8fd87c3cb86e
 
 # zfs dependencies
-github.com/containerd/zfs 2e6f60521b5690bf2f265c416a42b251c2a3ec8e
+github.com/containerd/zfs 9a0b8b8b5982014b729cd34eb7cd7a11062aa6ec
 github.com/mistifyio/go-zfs 166add352731e515512690329794ee593f1aaff2
 github.com/pborman/uuid c65b2f87fee37d1c7854c9164a450713c28d50cd
 

vendor/github.com/containerd/zfs/zfs.go

@@ -8,6 +8,7 @@ import (
 
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/mount"
+	"github.com/containerd/containerd/platforms"
 	"github.com/containerd/containerd/plugin"
 	"github.com/containerd/containerd/snapshots"
 	"github.com/containerd/containerd/snapshots/storage"
@@ -27,6 +28,8 @@ func init() {
 		Type: plugin.SnapshotPlugin,
 		ID:   "zfs",
 		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
+			ic.Meta.Platforms = append(ic.Meta.Platforms, platforms.DefaultSpec())
+			ic.Meta.Exports["root"] = ic.Root
 			return NewSnapshotter(ic.Root)
 		},
 	})