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/lib/evaluation_comment_email_spec.rb

@@ -1,7 +1,6 @@
 require "rails_helper"
 
 describe EvaluationCommentEmail do
-
   let(:author)        { create(:user) }
   let(:administrator) { create(:administrator) }
   let(:investment)    { create(:budget_investment, author: author, administrator: administrator) }
@@ -53,5 +52,4 @@ describe EvaluationCommentEmail do
       expect(comment_email.can_be_sent?).to be false
     end
   end
-
 end