go.net/websocket: update package comment to refer RFC 6455
go.net/websocket: update package comment to refer RFC 6455

Fixes issue 5222

R=golang-dev, mikioh.mikioh, minux.ma, r
CC=golang-dev
https://codereview.appspot.com/8651044

Committer: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

andrewzeneski/go.net,go-mirrors/go.net,polydawn-ports/go.net,gigq/go.net,fernandez14/go.net,ssor/go.net