Update kubeadm iptables cleanup command (#424)

- Repository URL changed
- Update version
- Update flag (see #278)

Author: Nicolas Perraut

docs/kubeadm.md

@@ -26,7 +26,7 @@ Now since kube-router provides service proxy as well. Run below commands to remo
 
 ```sh
 KUBECONFIG=/etc/kubernetes/admin.conf kubectl -n kube-system delete ds kube-proxy
-docker run --privileged --net=host gcr.io/google_containers/kube-proxy-amd64:v1.7.3 kube-proxy --cleanup-iptables
+docker run --privileged --net=host k8s.gcr.io/kube-proxy-amd64:v1.10.2 kube-proxy --cleanup
 ```