unknown directive "concat" in /etc/nginx/vhosts/www.test.com:10

[Shacho]

在ubuntu 中使用时候报的错误， www,test,com 是一个站点的配置，如：
server{
listen 80;
server_name www.test.com;

    access_log /home/xiechao/test/test.log;
    location / {
        root  /home/xiechao/test/;
        index index.html;
    }
    location /css/ {concat on;}

    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /usr/share/nginx/html;
    }

}