Fix logout code snippet for Kotlin: Corrected deleteCookies syntax

docs/modules/ROOT/pages/servlet/authentication/logout.adoc

@@ -226,7 +226,7 @@ Kotlin::
 ----
 http {
     logout {
-        deleteCookies = "our-custom-cookie"
+        deleteCookies("our-custom-cookie")
     }
 }
 ----