Return an :ok on the cookie security setup

[bianchidotdev]

Just a tiny usability thing. Happy to submit a PR myself.

Currently, the cookie security module's setup ends on building a plug connection. It's just a little strange that the return value from the cell is the actual Plug.Conn struct. Assuming the cell completes, it would probably be better to just return an :ok like the other modules

[houllette]

Thanks for the callout, @michaeldbianchi! We will be sure to include this in a planned upcoming release, but you're more than welcome to submit a PR yourself before that if you'd like to see it included sooner and/or are itching to add your name to the contributors list 😄