explicitly use Range.new/3 when counting down

[ericmooney-at-angel]

Summary of changes

With recent versions of Elixir, a runtime warning comes up when using first..last notation when first is greater than last.
Example:

warning: Range.new/2 and first..last default to a step of -1 when last < first. Use Range.new(first, last, -1) or first..last//-1, or pass 1 if that was your intention
  (tzdata 1.1.2) lib/tzdata/util.ex:99: Tzdata.Util.first_weekday_of_month_at_most/4
  (tzdata 1.1.2) lib/tzdata/period_builder.ex:356: anonymous fn/2 in Tzdata.PeriodBuilder.sort_rules_by_time/2
  (elixir 1.18.2) lib/enum.ex:1714: Enum."-map/2-lists^map/1-1-"/2
  (tzdata 1.1.2) lib/tzdata/period_builder.ex:356: Tzdata.PeriodBuilder.sort_rules_by_time/2
  (tzdata 1.1.2) lib/tzdata/period_builder.ex:228: Tzdata.PeriodBuilder.calc_rule_periods/8

This change simply uses the explicit Range.new/3 operator specifying -1 for the step.

Related doc:
https://hexdocs.pm/elixir/1.15.0/Range.html#new/2

Because of the simplicity and small size of this change, I thought it appropriate to merge into @nathany-copia 's excellent ongoing work to bring Timex up to date.

[ericmooney-at-angel]

Ah, please disregard, missed that this was already in this branch w/ the //-1 notation.

[nathany-copia]

Yup, see bitwalker#772