Fix reference to `luca`
Fix reference to `luca`

When the mailer is called, you pass an instance called `luca`

    InvoiceMailer.deliver(user: luca)

In the rest of the documentation, instead, the instance is called `user`. I fixed the reference name and decided to go with `luca` to make the code more explicit as the following can be a little bit more confusing to beginners

    InvoiceMailer.deliver(user: user)
hanami/mailer,hanami/mailer,lotus/mailer,lotus/mailer,hanami/mailer