Spanish build is broken

[OriolAbril]

We should also add doc previews for the different languages to prevent this from happening

Ref: https://readthedocs.org/projects/pymc-data-umbrella-es/builds/19524833/

[symeneses]

Seeing the logs the error is in about/intro_to_array_operations/notebook :

nbformat.reader.NotJSONError: Notebook does not appear to be JSON: 'Introducción a las operaciones con arre..

However, I don't see any suspicious translation in this resource.

[OriolAbril]

Partial fix in #189. No idea yet about what to do to get an actual fix