Fix zabbix_script_exec datastore

Author: wvu

modules/exploits/multi/http/zabbix_script_exec.rb

@@ -79,7 +79,7 @@ def exploit
     req = c.request_cgi({
       'method' => 'POST',
       'uri' => '/zabbix/',
-      'data' => 'request=&name=' << datastore['USERNAME'] << '&password=' << datastore['PASSWORD'] << '&enter=Sign+in'
+      'data' => "request=&name=#{datastore['USERNAME']}&password=#{datastore['PASSWORD']}&enter=Sign+in"
     })
 
     login = c.send_recv(req.to_s.sub("Host:", "Host: " << datastore["RHOST"]))