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

spec/controllers/legislation/annotations_controller_spec.rb

@@ -1,9 +1,7 @@
 require "rails_helper"
 
 describe Legislation::AnnotationsController do
-
   describe "POST create" do
-
     let(:legal_process) do
       create(:legislation_process, allegations_start_date: Date.current - 3.days,
              allegations_end_date: Date.current + 2.days)
@@ -162,6 +160,5 @@ describe Legislation::AnnotationsController do
       expect(annotation.reload.comments_count).to eq(2)
       expect(annotation.comments.last.body).to eq("una anotacion")
     end
-
   end
 end