Fixed relation

Hey Michael,

Here's a diff of some of the things we talked about today. Feel free to merge this into your codebase or just use it for reference. Getting used to pull requests and code reviews (like this) is a really handy skill to have.

One thing we didn't talk about was using the `debugger` gem which I added to your Gemfile. Here's the Rails guide on how to use it: http://guides.rubyonrails.org/debugging_rails_applications.html#debugging-with-the-debugger-gem

// Jason
You can do this either way, but I think this way gives you a better default message in `article.errors.full_messages`