Banea Dominios

Creating logic for banning specific email domains.
For me, it's clearer
`Modera::BaneaDominio.pluck(:dominio).include? dominio.downcase`
(and you can drop the .lista method)

because at the first glance I though that lista was a string kind of "trashmail.com, mierdacorreo.com, ....", which will have different behavior (it will wrongly declarate `ashmail.com` as non valid).