Can't upgrade from Trisquel Mini 7 to 8

Hi,

I'm having this situation, any ideas/recommendations?

```
$ sudo do-release-upgrade
...
No se ha podido calcular la actualización

Ha ocurrido un problema mientras se calculaba la actualización.

Eso se ha podido causar por:
* Actualizar a una versión de Trisquel aún no publicada
* Estar ejecutando la versión actual, aún no publicada, de Trisquel
* Paquetes no oficiales de software no proporcionados por Trisquel

If none of this applies, then please report this bug using the
command https://trisquel.info/en/project/issues in a browser..
```

System is in Spanish, the translation would be something like:

```
The update could not be calculated

A problem occurred while the update was being calculated.

This could have been caused by:
* Upgrade to a version of Trisquel not yet published
* Be running the current version, not yet published, of Trisquel
* Unofficial software packages not provided by Trisquel

If none of this applies, then please report this bug using the
command https://trisquel.info/en/project/issues in a browser ..
```

I'm having a good number of:

Error http://fr.archive.trisquel.info belenos-security/main Translation-es_AR

Error http://fr.archive.trisquel.info belenos-updates/main Translation-en

Error http://fr.archive.trisquel.info belenos-updates/main Translation-es

Error http://fr.archive.trisquel.info belenos-updates/main Translation-es_AR
---

Maybe an issue with non-existent mirrors?

Any help is most welcome.

Thanks a lot.