Fix POST content type for Firefox. Same as https://github.com/LearnBoost/socket.io/pull/806 but for Engine.io
Fix POST content type for Firefox. Same as https://github.com/LearnBoost/socket.io/pull/806 but for Engine.io

socketio/engine.io,nkzawa/engine.io,socketio/engine.io,kapouer/engine.io,CantemoInternal/engine.io