small modifications for rails 5 api flag

[jlr7245]

Thanks so much for the tutorial, it was great and worked with a few slight modifications.

I had to rename the token column to auth_token (so, rails g model user name auth_token email password_digest). This of course meant I had to change token to auth_token in a number of places: api_controller.rb, sessions_controller.rb, models/user.rb.

I was using a postgresql database and as @jaeming in #1 mentioned had to modify the migration: create the user table first and then, in a separate migration, add the index.

In sessions_controller.rb, I had to change user.regenerate_token to user.regenerate_auth_token.

And I had to modify the ApplicationController to look like this:

class ApplicationController < ActionController::API
    include ActionController::HttpAuthentication::Token::ControllerMethods
end

(I'm being as explicit as possible about my modifications because I suspect some of my students will find this tutorial and run into all the exact same bugs I did 😉 )