fix --etcd-servers flag

debian/services/lib.sh

@@ -24,5 +24,5 @@ set_public_ip() {
 set_etcd_params() {
     local default_etcd_server="etcd.${DOMAIN}"
     ETCD_SERVER="${ETCD_SERVER:-${default_etcd_server}}"
-    ETCD_OPTIONS="${ETCD_OPTIONS} --etcd-server=localhost:4001,${ETCD_SERVER}"
+    ETCD_OPTIONS="${ETCD_OPTIONS} --etcd-servers=localhost:4001,${ETCD_SERVER}"
 }