Update cluster.asciidoc

Fixed asciidoc on cluster module page

docs/reference/modules/cluster.asciidoc

@@ -39,23 +39,31 @@ The following settings may be used:
 
 Controls shard allocation for all indices, by allowing specific
 kinds of shard to be allocated.
-
++
+--
 Can be set to:
-    * `all` (default) - Allows shard allocation for all kinds of shards.
-    * `primaries` - Allows shard allocation only for primary shards.
-    * `new_primaries` - Allows shard allocation only for primary shards for new indices.
-    * `none` - No shard allocations of any kind are allowed for all indices.
+
+[horizontal]
+
+`all`:: (default) Allows shard allocation for all kinds of shards.
+`primaries`::  Allows shard allocation only for primary shards.
+`new_primaries`:: Allows shard allocation only for primary shards for new indices.
+`none`::No shard allocations of any kind are allowed for all indices.
+--
 
 `cluster.routing.rebalance.enable`::
 
 Controls shard rebalance for all indices, by allowing specific
 kinds of shard to be rebalanced.
-
++
+--
 Can be set to:
-    * `all` (default) - Allows shard balancing for all kinds of shards.
-    * `primaries` - Allows shard balancing only for primary shards.
-    * `replicas` - Allows shard balancing only for replica shards.
-    * `none` - No shard balancing of any kind are allowed for all indices.
+
+`all`:: (default) Allows shard balancing for all kinds of shards.
+`primaries`:: Allows shard balancing only for primary shards.
+`replicas`:: Allows shard balancing only for replica shards.
+`none`:: No shard balancing of any kind are allowed for all indices.
+--
 
 `cluster.routing.allocation.same_shard.host`::
       Allows to perform a check to prevent allocation of multiple instances