doc: fix document example error
//
// func etcdDelete(c *clientv3, service, addr string) error {
// r := &etcdnaming.GRPCResolver{Client: c}
-// return r.Update(c.Ctx(), "my-service", naming.Update{Op: naming.Delete, Addr: "1.2.3.4"})
+// return r.Update(c.Ctx(), service, naming.Update{Op: naming.Delete, Addr: "1.2.3.4"})
// }
//
// Or register an expiring endpoint with a lease:
