upgrade kubefed client to v0.6.1

Signed-off-by: yuswift <yuswiftli@yunify.com>

vendor/sigs.k8s.io/kubefed/pkg/controller/util/worker.go

@@ -137,7 +137,7 @@ func (w *asyncWorker) deliver(qualifiedName QualifiedName, delay time.Duration,
 	key := qualifiedName.String()
 	if failed {
 		w.backoff.Next(key, time.Now())
-		delay = delay + w.backoff.Get(key)
+		delay += w.backoff.Get(key)
 	} else {
 		w.backoff.Reset(key)
 	}