range_combiner.rb

months = [1,2,3,4,5,6,7,9,10,11,12].to_a.map { |month| Date.new(2018, month) }
months = months.map { |month| month..month.end_of_month }
months.inject([]) do |array, month|
  if array.present? && array.last.last + 1.day == month.first
    array.push(array.pop.first..month.last)
  else
    array.push(month)
  end
end.map do |range|
  [range.first.strftime("%b '%y"), range.last.beginning_of_month.strftime("%b '%y")].join(" - ")
end.join(" and ")