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/models/map_validations.rb

@@ -1,9 +1,7 @@
 shared_examples "map validations" do
-
   let(:mappable) { build(model_name(described_class)) }
 
   describe "validations" do
-
     before do
       Setting["feature.map"] = true
     end
@@ -43,11 +41,9 @@ shared_examples "map validations" do
 
       expect(mappable).not_to be_valid
     end
-
   end
 
   describe "cache" do
-
     it "expires cache when the map is updated" do
       map_location = create(:map_location)
       mappable.map_location = map_location
@@ -56,7 +52,5 @@ shared_examples "map validations" do
       expect { map_location.update(latitude: 12.34) }
         .to change { mappable.reload.updated_at }
     end
-
   end
-
 end