title: Can't subscribe to page's likes through Real-time updates API
body: <p>I am trying to get updates when the like count of a page my app is on is updated. I am trying to accomplish this by using the <a href="https://developers.facebook.com/docs/reference/api/realtime/" rel="nofollow">FB Real-time Updates API</a></p>
  
  <p>When I do a POST, with the object = "page" and the fields = "likes", I get a 400 error with the message '"likes" is an invalid field name'.</p>
  
  <p>object = "page" and the fields = "name" works fine.</p>
  
  <p>The documentation states you are allowed to subscribe to any public attribute.</p>
  
  <p>For those playing the home game, here are the steps to reproduce the problem:</p>
  
  <ol>
  <li><p>Get an OAuth token for your app:</p>
  
  <p><code>https://graph.facebook.com/oauth/access_token?client_id=&lt;app_id&gt;&amp;client_secret=&lt;secret&gt;&amp;grant_type=client_credentials</code></p></li>
  <li><p>Post to subscription URL:</p>
  
  <p><code>https://graph.facebook.com/&lt;app_id&gt;/subscriptions</code></p></li>
  </ol>
  
  <p>POST Variables:</p>
  
  <pre><code>'access_token' =&gt; `&lt;access token from step 1&gt;`,
  'object' =&gt; 'page',
  'fields' =&gt; 'likes',
  'callback_url' =&gt; `&lt;a callback url&gt;`,
  'verify_token' =&gt; 'testingstring123'
  </code></pre>