heroku labs:enable websockets is no longer necesarry

[valentinvieriu]

Heroku enabled the the websockets automatically for all applications. See https://blog.heroku.com/archives/2014/7/7/websockets_now_ga
We don't need to enable the lab option ( it would not work anyway ).

Also as I'm seeing in #369 we will need to add DOMAIN as a variable to heroku too:
heroku config:set DOMAIN=customDomainChoosed.herokuapp.com

[meeDamian]

@valentinvieriu Good point, I completely forgotten about it! I'll add it to README.

[meeDamian]

@valentinvieriu See #396