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/nested_documentable.rb

@@ -22,7 +22,6 @@ shared_examples "nested documentable" do |login_as_name, documentable_factory_na
   end
 
   describe "at #{path}" do
-
     scenario "Should show new document link when max documents allowed limit is not reached" do
       login_as user_to_login
       visit send(path, arguments)
@@ -304,9 +303,7 @@ shared_examples "nested documentable" do |login_as_name, documentable_factory_na
         expect(page).not_to have_content("Add new document")
       end
     end
-
   end
-
 end
 
 def documentable_redirected_to_resource_show_or_navigate_to