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/models/comment_spec.rb

@@ -1,7 +1,6 @@
 require "rails_helper"
 
 describe Comment do
-
   let(:comment) { build(:comment) }
 
   it_behaves_like "has_public_author"
@@ -44,7 +43,6 @@ describe Comment do
   end
 
   describe "#confidence_score" do
-
     it "takes into account percentage of total votes and total_positive and total negative votes" do
       comment = create(:comment, :with_confidence_score, cached_votes_up: 100, cached_votes_total: 100)
       expect(comment.confidence_score).to eq(10000)
@@ -81,7 +79,6 @@ describe Comment do
         expect(previous).to be > comment.confidence_score
       end
     end
-
   end
 
   describe "cache" do