title: as_json issue with include tables
body: <p>I have the following models.</p>
  
  <pre><code>class User &lt; ActiveRecord::Base
    has_many :kriya_sessions
  end
  
  class KriyaSession &lt; ActiveRecord::Base
    belongs_to :user
  end
  </code></pre>
  
  <p>in my users controller I'm trying like</p>
  
  <pre><code>def user_sessions
    @users = User.all
    render json: @users.as_json(include: [:kriya_sessions])
  end
  </code></pre>
  
  <p>But in my response I don't see any kriya_sessions object in my user object. Can someone tell me where am I doing wrong?</p>