Updated the kube-proxy cleanup command to use the newer version (#762)

LGTM. Thanks for the pr @zerkms

Author: zerkms

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 -v /lib/modules:/lib/modules --net=host k8s.gcr.io/kube-proxy-amd64:v1.10.2 kube-proxy --cleanup
+docker run --privileged -v /lib/modules:/lib/modules --net=host k8s.gcr.io/kube-proxy-amd64:v1.15.1 kube-proxy --cleanup
 ```