Detect protect attributes for rails 4

I'm not 100% sure about this approach, or hanging it off of `::PaperTrail`, but I needed this to prevent the following error in a Rails 4 application

```
activemodel-4.0.0/lib/active_model/deprecated_mass_assignment_security.rb:14:
in `attr_accessible': `attr_accessible` is extracted out of Rails into a gem. Please use new recommended protection model for params(strong
_parameters) or add `protected_attributes` to your Gemfile to use old one. (RuntimeError)
```

straight outta `lib/paper_trail/version.rb:5`