Better way to negotiate the WebSocket protocol

[spacemeowx2]

seanmonstar/warp#496

In the warp_subscriptions example, the playground cannot connect to the server via WebSocket because the WebSocket implementation in wrap has a unconfigurable Sec-WebSocket-Protocol header. Currently we can do a workaround adding the header manually.

[cloudsftp]

Is this till current?
The example seems to work w/o the workaround

[tyranron]

Fixed by auto-negotiating Sec-WebSocket-Protocol in #1191.