how can i fix this how to fix [09:14:19 WARN]: ** SERVER IS RUNNING IN OFFLINE/INSECURE MODE! [09:14:19 WARN]: The server will make no attempt to authenticate usernames. Beware. [09:14:19 WARN]: Whilst this makes it possible to use BungeeCord, unless access to your server is properly restricted, it also opens up the ability for hackers to connect with any username they choose. [09:14:19 WARN]: Please see http://www.spigotmc.org/wiki/firewall-guide/ for further information. [09:14:19 WARN]: To change this, set "online-mode" to "true" in the server. Properties file. when i do it it and restart server it just goes back to false