/area build

Since upstream gorilla websocket changed SetCloseHandler to handle a returned error from WriteControl():

https://github.com/gorilla/websocket/blob/666c197fc9157896b57515c3a3326c3f8c8319fe/conn.go#L1166-L1168

serving's unit test TestServerShutdown() started failing as websocket does not return CloseError.
We temporary pin to gorilla websocket to 1.5.0 but should be fixed.

Please refer to #14588 for the error log.