fix bug

Author: firefart

modules/exploits/multi/http/mantisbt_php_exec.rb

@@ -91,7 +91,7 @@ def do_login()
       })
       fail_with(Failure::NoAccess, 'Login failed') unless res && res.code == 302
 
-      fail_with(Failure::NoAccess, 'Wrong credentials') unless res && res.redirection.to_s.include?('login_page.php')
+      fail_with(Failure::NoAccess, 'Wrong credentials') unless res && !res.redirection.to_s.include?('login_page.php')
 
       session_cookie = "#{session_cookie} #{res.get_cookies}"
     end