Override static asset cache expiration on Heroku.

gistfile1.rb

# Stick the following in an initializer.

module Heroku
  class StaticAssetsMiddleware
    def cache_static_asset(reply)
      return reply unless can_cache?(reply)

      status, headers, response = reply

      headers['Cache-Control'] = 'public, max-age=31556926' # 1 year

      build_new_reply(status, headers, response)
    end
  end
end