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/helpers/admin_helper_spec.rb

@@ -1,9 +1,7 @@
 require "rails_helper"
 
 describe AdminHelper do
-
   describe "#admin_submit_action" do
-
     it "returns new when the the resource has not been persisted" do
       poll = build(:poll)
       expect(admin_submit_action(poll)).to eq("new")
@@ -13,7 +11,5 @@ describe AdminHelper do
       poll = create(:poll)
       expect(admin_submit_action(poll)).to eq("edit")
     end
-
   end
-
 end