Update link text in welcome-app-gateway.yml

Author: gitanjali1993

support/azure/application-gateway/welcome-app-gateway.yml

@@ -22,5 +22,5 @@ landingContent:
     linkLists:
       - linkListType: how-to-guide
         links:
-          - text: Azure API is returning blank response
+          - text: ApplicationGatewaySkuNotSpecified error
             url: error-codes/applicationgatewayskunotspecified.md