Fix improved error handling

Author: mpizala

modules/exploits/linux/http/docker_daemon_tcp.rb

@@ -144,7 +144,7 @@ def check
 
   def exploit
     # check if target is vulnerable
-    unless check == Exploit::CheckCode::Appears
+    unless check == Exploit::CheckCode::Vulnerable
       fail_with(Failure::Unknown, 'Failed to connect to the target')
     end