Padrino should respond to env and root

[tily]

Summary

• In lib/config/integrations/sinatra.rb, Padrino.env and Padrino.root is called without respond_to? check
• But there are cases where only padrino-helpers is depended on, and Padrino.env and Padrino.root are not available, like kaminari-sinatra
  • See https://github.com/kaminari/kaminari-sinatra/blob/master/kaminari-sinatra.gemspec#L34

[pkuczynski]

Thanks!