Use the --dry-run mode to avoid to stop the server when no update is available

[lgnap]

Hello,

For the moment I have to stop the factorio server just in case of new update is available (the binary doesn't allow to self update if running). I think that return a error/shell/return code != 0 if new version available in dry-run mode could be interesting before really stop the server and effectively run the update.

Thanks

[narc0tiq]

Makes sense to me.