def distance
      return nil unless @locations.size > 1
      locations.each_cons(2).reduce(0) do |acc, (loc1, loc2)|
        acc + loc1.distance_to(loc2)
      end
    end
def distance
      return nil unless @locations.size > 1
      locations.each_cons(2).reduce(0) do |acc, (loc1, loc2)|
        acc + loc1.distance_to(loc2)
      end
    end
Give the distance in meters between ordered
 location points using the 'Haversine' formula