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/mailers/dashboard/mailer_spec.rb

@@ -40,11 +40,9 @@ describe Dashboard::Mailer do
       expect(email).to have_body_text("Share in")
       expect(email).to have_body_text(proposal_path(proposal))
     end
-
   end
 
   describe "#new_actions_notification rake task" do
-
     before do
       Rake.application.rake_require "tasks/dashboards"
       Rake::Task.define_task(:environment)
@@ -150,7 +148,6 @@ describe Dashboard::Mailer do
   end
 
   describe "#new_actions_notification_on_create" do
-
     before do
       ActionMailer::Base.deliveries.clear
     end
@@ -214,7 +211,6 @@ describe Dashboard::Mailer do
   end
 
   describe "#new_actions_notification_on_published" do
-
     before do
       ActionMailer::Base.deliveries.clear
 
@@ -273,5 +269,4 @@ describe Dashboard::Mailer do
       expect(email).to have_body_text("Go ahead, discover them!")
     end
   end
-
 end