Downgrade kombu from 4.6.5 to 4.6.3
Downgrade kombu from 4.6.5 to 4.6.3

As suggested in https://github.com/celery/kombu/issues/1063
This should fixes the issue with redis key getting evicted every now and then
and should mean we stop receiving the following error:
Control command error: OperationalError(u"\nCannot route message for exchange u'reply.celery.pidbox': Table empty or key no longer exists.\nProbably the key (u'_kombu.binding.reply.celery.pidbox') has been removed from the Redis database.\n",)

ministryofjustice/laa-legal-adviser-api,ministryofjustice/laa-legal-adviser-api,ministryofjustice/laa-legal-adviser-api