Go to gem file:
gem 'omniauth-facebook', '~> 4.0.0'
in terminal - bundle for updating omniauth-facebook ('bundle update' can broke your application, because it's updated all your gems).
Push changes to the production server.
RESTART PRODUCTION SERVER
In my case:
I'm updated from 2.0.1 to 4.0.0
All works fine, but you have restart production server (stop and start unicorn or comething).