docs: restore the upgrade mechanism in v4
After re-reading the goals of Engine.IO [1], it seems the upgrade mechanism is better for the user experience, so we'll keep that way. [1] https://github.com/socketio/engine.io#goals
D
Damien Arrachequesne committed
660263fae230cc48da8ba2b030ef6518343a972a
Parent: cf3a759