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/shared/features/imageable.rb

@@ -19,7 +19,6 @@ shared_examples "imageable" do |imageable_factory_name, imageable_path, imageabl
   end
 
   context "Show" do
-
     scenario "Show descriptive image when exists", :js do
       image = create(:image, imageable: imageable)
 
@@ -35,7 +34,6 @@ shared_examples "imageable" do |imageable_factory_name, imageable_path, imageabl
 
       expect(page).to have_content image.title
     end
-
   end
 end