fix add record error

Add single quote for --record-set-name parameter. 
Without that, it will get an error: *az: error: unrecognized arguments: demo*.

Author: sheng-jie

articles/aks/ingress-tls.md

@@ -82,7 +82,7 @@ Add an *A* record to your DNS zone with the external IP address of the NGINX ser
 az network dns record-set a add-record \
     --resource-group myResourceGroup \
     --zone-name MY_CUSTOM_DOMAIN \
-    --record-set-name * \
+    --record-set-name '*' \
     --ipv4-address MY_EXTERNAL_IP
 ```