chore(updater): set vpn field for all providers

- Bump servers model versions for all providers except mullvad, ivpn, windscribe
- Do not leave `vpn` JSON field empty for any server

internal/updater/providers/nordvpn/servers.go

@@ -9,6 +9,7 @@ import (
 	"net"
 	"net/http"
 
+	"github.com/qdm12/gluetun/internal/constants/vpn"
 	"github.com/qdm12/gluetun/internal/models"
 )
 
@@ -45,6 +46,7 @@ func GetServers(ctx context.Context, client *http.Client, minServers int) (
 		}
 
 		server := models.Server{
+			VPN:      vpn.OpenVPN,
 			Region:   jsonServer.Country,
 			Hostname: jsonServer.Domain,
 			Number:   number,