websocket: use of crypto/rand package in test
websocket: use of crypto/rand package in test

The Read function of math/rand package doesn't exist on Go 1.5 or below.

Change-Id: If837bbd0a862726be93e07b021701004ba0f0fad
Reviewed-on: https://go-review.googlesource.com/30896
Run-TryBot: Mikio Hara <e2f4d2eec1d9a1f781345cdd7260d7d52e6468ae@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/net