Fix in WAFlogQuery

Author: piotrgradzinski

articles/web-application-firewall/afds/waf-front-door-monitor.md

@@ -34,7 +34,7 @@ The following example query obtains WAF logs on blocked requests:
 ``` WAFlogQuery
 AzureDiagnostics
 | where ResourceType == "FRONTDOORS" and Category == "FrontdoorWebApplicationFirewallLog"
-| where action_name_s == "Block"
+| where action_s == "Block"
 
 ```