Documentation: fix "Missing infra1="

Documentation: fix "Missing infra1="

Documentation/clustering.md

@@ -30,7 +30,7 @@ ETCD_INITIAL_CLUSTER_STATE=new
 ```
 
 ```
--initial-cluster infra0=http://10.0.1.10:2380,http://10.0.1.11:2380,infra2=http://10.0.1.12:2380 \
+-initial-cluster infra0=http://10.0.1.10:2380,infra1=http://10.0.1.11:2380,infra2=http://10.0.1.12:2380 \
   -initial-cluster-state new
 ```