Update 4-authentication.md
Update 4-authentication.md

* bump bcrypt version
* update instructions for generating the UserType
* remove a blank line
* replace find_by(id: id) with find(id)
* remove instruction for removing _
* rename AuthProviderEmailInput to AuthProviderCredentialsInput
* add `:field` argument to Mutations::CreateUser.new in tests

howtographql/howtographql,howtographql/howtographql,howtographql/howtographql