Update http-response-codes.md

Modified this part to clarify: backend response changed to backend response time 
#### 504 – Request timeout

HTTP 504 errors are presented if a request is sent to application gateways using V2 SKU, and the backend response time exceeds the time-out value associated to the listener's rule. This value is defined in the HTTP setting.

Author: asukumar22

articles/application-gateway/http-response-codes.md

@@ -99,8 +99,8 @@ For information about scenarios where 502 errors occur, and how to troubleshoot
 
 #### 504 – Request timeout
 
-HTTP 504 errors are presented if a request is sent to application gateways using v2 sku, and the backend response exceeds the time-out value associated to the listener's rule. This value is defined in the HTTP setting.
+HTTP 504 errors are presented if a request is sent to application gateways using v2 sku, and the backend response time exceeds the time-out value associated to the listener's rule. This value is defined in the HTTP setting.
 
 ## Next steps
 
-If the information in this article doesn't help to resolve the issue, [submit a support ticket](https://azure.microsoft.com/support/options/).
+If the information in this article doesn't help to resolve the issue, [submit a support ticket](https://azure.microsoft.com/support/options/).