lib/mako/subscription_list_writer.rb
def append_and_write
      contents = append_and_render
      File.open(destination, 'w+', encoding: 'utf-8') do |f|
        f.write(contents)
      end
    end
def append_and_write
      contents = append_and_render
      File.open(destination, 'w+', encoding: 'utf-8') do |f|
        f.write(contents)
      end
    end
Appends the new subscriptions to the subscription list and
 writes the results out to the file.