fix wsgi by returning bytes
fix wsgi by returning bytes

JamesAwesome/marathon-lb,knesenko/marathon-lb,JamesAwesome/marathon-lb,matt-deboer/marathon-lb,vixns/marathon-lb,mesosphere/marathon-lb,JamesAwesome/marathon-lb,matt-deboer/marathon-lb,GrovoLearning/marathon-lb,knesenko/marathon-lb,GrovoLearning/marathon-lb,vixns/marathon-lb,knesenko/marathon-lb,mesosphere/marathon-lb,vixns/marathon-lb,GrovoLearning/marathon-lb,mesosphere/marathon-lb,matt-deboer/marathon-lb