Bump devise-encryptable to version that limits devise versions to stable

Fixes #80
Switch to spree namespace for translations
Fix request specs, failings down to 1

Add en.yml file with devise namespace entries. It feels odd to have
the devise namespace on spree core locale file since users can opt to
use other auth strategies or even have an already devise auth model.
Keeping those entries on spree core may confuse / override users
existing app devise locale entries

Fixes #85
Add travis config

This is useful for those who want to fork this project and be able to run the
tests.