16492: Upgrades websocket-extensions gem to fix a security alert.

16492: Upgrades websocket-extensions gem to fix a security alert.

We really don't use this gem as it's requested by actioncable from Rails 5
that we don't even load at runtime. But, as we cannot remove actioncable
from our Gemfile.lock files because of some other gems depending on 'rails',
we upgrade it to make GitHub happy.

Arvados-DCO-1.1-Signed-off-by: Lucas Di Pentima <lucas@di-pentima.com.ar>