Cleanup taxon promotion rule

Removes use of inject and unused variables

core/app/models/spree/promotion/rules/taxon.rb

@@ -49,7 +49,7 @@ def order_taxons(order)
 
  # ids of taxons rules and taxons rules children
  def taxons_including_children_ids
- taxons.inject([]){ |ids, taxon| ids += taxon.self_and_descendants.ids }
+ taxons.flat_map { |taxon| taxon.self_and_descendants.ids }
  end
 
  # taxons order vs taxons rules and taxons rules children
@@ -58,7 +58,7 @@ def order_taxons_in_taxons_and_children(order)
  end
 
  def taxons_in_order_including_parents(order)
- order_taxons_in_taxons_and_children(order).inject([]){ |taxons, taxon| taxons << taxon.self_and_ancestors }.flatten.uniq
+ order_taxons_in_taxons_and_children(order).flat_map(&:self_and_ancestors).uniq
  end
 
  def taxon_product_ids