Trisquel 10 System Update Problem

Hi guys,I installed Trisquel 10 and I could not system upgrade.
whenever i write to console "sudo apt update" take error message.
sudo apt update
(output)
Err:1 http://mirrors.serverhost.ro/trisquel/packages nabia InRelease
Could not resolve 'mirrors.serverhost.ro'
Err:2 http://mirrors.serverhost.ro/trisquel/packages nabia-security InRelease
Could not resolve 'mirrors.serverhost.ro'
Err:3 http://mirrors.serverhost.ro/trisquel/packages nabia-updates InRelease
Could not resolve 'mirrors.serverhost.ro'
Err:4 http://mirrors.serverhost.ro/trisquel/packages nabia-backports InRelease
Could not resolve 'mirrors.serverhost.ro'
Reading package lists... Done
Building dependency tree
Reading state information... Done
All packages are up to date.
W: Failed to fetch http://mirrors.serverhost.ro/trisquel/packages/dists/nabia/InRelease Could not resolve 'mirrors.serverhost.ro'
W: Failed to fetch http://mirrors.serverhost.ro/trisquel/packages/dists/nabia-security/InRelease Could not resolve 'mirrors.serverhost.ro'
W: Failed to fetch http://mirrors.serverhost.ro/trisquel/packages/dists/nabia-updates/InRelease Could not resolve 'mirrors.serverhost.ro'
W: Failed to fetch http://mirrors.serverhost.ro/trisquel/packages/dists/nabia-backports/InRelease Could not resolve 'mirrors.serverhost.ro'
W: Some index files failed to download. They have been ignored, or old ones used instead.