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

app/helpers/map_locations_helper.rb

@@ -1,5 +1,4 @@
 module MapLocationsHelper
-
   def map_location_available?(map_location)
     map_location.present? && map_location.available?
   end
@@ -66,5 +65,4 @@ module MapLocationsHelper
       options[:marker_longitude] = map_location.longitude if map_location.longitude.present?
       options
     end
-
 end