Client::pubSub() still works like usual by returning a new pub/sub
context, but it is now considered an alias of Client::pubSubLoop().
This change is necessary in preparation for the next major version
of Predis where Client::pubSub() will be used for the new PUBSUB
command introduced in Redis 2.8.
as per this change in predis:
https://github.com/nrk/predis/commit/8533dbdb0b3e3ee02d0eed474a09dcd659afb267