Add and apply rubocop rules for empty lines

We were very inconsistent regarding these rules.

Personally I prefer no empty lines around blocks, clases, etc... as
recommended by the Ruby style guide [1], and they're the default values
in rubocop, so those are the settings I'm applying.

The exception is the `private` access modifier, since we were leaving
empty lines around it most of the time. That's the default rubocop rule
as well. Personally I don't have a strong preference about this one.


[1] https://rubystyle.guide/#empty-lines-around-bodies

app/models/verification/email.rb

@@ -33,5 +33,4 @@ class Verification::Email
   def self.valid_token?(user, token)
     Devise.token_generator.digest(User, :email_verification_token, user.email_verification_token) == token
   end
-
 end

app/models/verification/letter.rb

@@ -51,5 +51,4 @@ class Verification::Letter
     def generate_verification_code
       rand(100000..999999).to_s
     end
-
 end

app/models/verification/management/document.rb

@@ -49,5 +49,4 @@ class Verification::Management::Document
   def verify
     user.update(verified_at: Time.current) if user?
   end
-
 end

app/models/verification/management/managed_user.rb

@@ -6,5 +6,4 @@ class Verification::Management::ManagedUser
     find_or_initialize_by(document_type:   document_type,
                           document_number: document_number)
   end
-
 end

app/models/verification/residence.rb

@@ -87,5 +87,4 @@ class Verification::Residence
     def clean_document_number
       self.document_number = document_number.gsub(/[^a-z0-9]+/i, "").upcase if document_number.present?
     end
-
 end