Rails4 last build fix and warning

This PR get us a green build on rails4 branch :beers: and with very few warnings this time

I'll keep an eye on deface, ransack and awesome_nested_set for release candidates. I think ransack build was green last time I checked, deface build has an error I can't explain yet and awesome_nested_set probably needs some more help.

This is what we need to add to the Gemfile on a rails 4 app to get Spree running:

```
gem 'spree', github: 'spree/spree', branch: 'rails4'
gem 'spree_auth_devise', github: 'spree/spree_auth_devise', branch: 'rails4'
gem 'deface', github: 'huoxito/deface', branch: 'rails4'
gem 'ransack', github: 'ernie/ransack', branch: 'rails-4'
gem 'awesome_nested_set', github: 'huoxito/awesome_nested_set', branch: 'rails4'
```

feedback much appreciated