nginx proxy 支持 WebSocket

参考：https://www.nginx.com/blog/websocket-nginx/

nginx 中需要配置如下的选项，就可以支持代理 WebSocket

location /wsapp/ {
    proxy_pass http://wsbackend;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "Upgrade";
    proxy_set_header Host $host;
}