Update diagnose-unassigned-shards.md (#3036)

👋 howdy, team! In order to return JSON as response suggests, the CAT
Shards API neesd `&format=json`. TIA! 🙏

Co-authored-by: David Kilfoyle <[email protected]>

Author: stefnestor

troubleshoot/elasticsearch/diagnose-unassigned-shards.md

@@ -45,7 +45,7 @@ In order to diagnose the unassigned shards, follow the next steps:
 4. View the unassigned shards using the [cat shards API](https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-cat-shards).
 
     ```console
-    GET _cat/shards?v=true&h=index,shard,prirep,state,node,unassigned.reason&s=state
+    GET _cat/shards?v=true&h=index,shard,prirep,state,node,unassigned.reason&s=state&format=json
     ```
 
     The response will look like this: