Land rapid7#5170, fail_with argument fix

Author: wvu

modules/exploits/unix/webapp/wp_worktheflow_upload.rb

@@ -67,7 +67,7 @@ def exploit
         fail_with("#{peer} - Unable to deploy payload, server returned #{res.code}")
       end
     else
-      fail_with('ERROR')
+      fail_with(Failure::Unknown, 'ERROR')
     end
 
     print_status("#{peer} - Calling payload...")