Update: rename `shouldNotBeLoggedIn` to `isLoggedOut`

[Ironhack Education Team]

Since we already have isLoggedIn middleware, as an opposite one we should follow the same naming convention.

Any thoughts on this one @itstheandre?

[André de Albuquerque]

Good catch. I like that. Initially we named it because it was in flow of class. But isLoggedOut is a far better name. Fixed 👍