Update _verify_keeper_using_mntr.mdx

docker command must be run as `/bin/sh -c 'c....'` otherwise the command past '|' will be executed on the locally and not on the container. Additionally, instead of localhost should 127.0.0.1 should be use. Bu default localhost resolves to `::1` on the recent clickhouse-keeper image, while only 127.0.0.1 listens.

Author: afpd

docs/deployment-guides/replication-sharding-examples/_snippets/_verify_keeper_using_mntr.mdx

@@ -16,7 +16,7 @@ Run the command below from a shell on `clickhouse-keeper-01`, `clickhouse-keeper
 for `clickhouse-keeper-01` is shown below:
 
 ```bash
-docker exec -it clickhouse-keeper-01 echo mntr | nc localhost 9181
+docker exec -it clickhouse-keeper-01  /bin/sh -c 'echo mntr | nc 127.0.0.1 9181'
 ```
 
 The response below shows an example response from a follower node:
@@ -67,4 +67,4 @@ zk_max_file_descriptor_count    18446744073709551615
 zk_followers    2
 zk_synced_followers     2
 # highlight-end
-```
+```