1.1.21 (17/09/17)

• update (bundled) rack to 1.6.8
• add Rack::Handler::Servlet::DefaultEnv#get_header (#212)
  missing methods to handle ActionController::Base#reset_session
• can only safely stream natively on ActionDispatch <= 3.2 (#210)
  (broken Rails streaming for Rails 4.x)
• when handling OPTION calls ignore both 'Date' and 'Allow' headers (#205)