def sequence
      if @version_class.primary_key_is_int?
        @versions.select(primary_key).order(primary_key.asc)
      else
        @versions.
          select([table[:created_at], primary_key]).
          order(@version_class.timestamp_sort_order)
      end
    end
def sequence
      if @version_class.primary_key_is_int?
        @versions.select(primary_key).order(primary_key.asc)
      else
        @versions.
          select([table[:created_at], primary_key]).
          order(@version_class.timestamp_sort_order)
      end
    end
Returns `@versions` in chronological order.
 @api private