title: getstram.io update activity does not move it up the feed
body: <p>Assuming I have a music app (like the example) using GetStream.io feeds, where I have user feeds and band feeds (user being able to follow other users, or bands).
  I am using the stram-ruby gem.</p>
  
  <p>Now, say I am posting as a user to a band feed, doing something like:</p>
  
  <pre><code>user_feed = @client.feed('user', user_id)
  activity_data = {
      :actor =&gt; "User:#{user_id}",
      :verb =&gt; 'post',
      :object =&gt; "Post:#{post.id}",
      :target =&gt; "Band:#{band_id}",
      :foreign_id =&gt; "Post:#{post.id}",
      :time =&gt; post.created_at.as_json,
      :comment =&gt; 'comment 1',
      :to =&gt; ["band:#{band_id}"]
  }
  user_feed.add_activity(activity_data)
  </code></pre>
  
  <p>This works fine, and retrieving the band feed, I can see that post:</p>
  
  <pre><code>@client.feed('band', band_id).get()
  </code></pre>
  
  <p>Now, I am attempting to update this entry (using the comment field just to see something changes):</p>
  
  <pre><code>activity_data = {
      :actor =&gt; "User:#{user_id}",
      :verb =&gt; 'post',
      :object =&gt; "Post:#{post.id}",
      :target =&gt; "Band:#{band_id}",
      :foreign_id =&gt; "Post:#{post.id}",
      :time =&gt; post.created_at.as_json,
      :comment =&gt; 'comment 2',
      :to =&gt; ["band:#{band_id}"]
  }
  @client.update_activity(activity_data)
  </code></pre>
  
  <p>getting the band feed will show correctly the new comment ('comment 2'), but my problem is this:</p>
  
  <ol>
  <li>I am using the created_at field of my post (to ensure my ability to update it as GetStream docs say this is part of the unique key)</li>
  <li>I use the same created_at time on the update</li>
  <li>When fetching the band feed, I would expect this activity to be the top one - as the feed should be sorted chronologically. But it remains where it was before based on the created_at time.</li>
  </ol>
  
  <p>What to do?</p>
  
  <p>I can try using the updated_at field of the post, but then, if for any reason the post in my DB changes without me updating the GetStream feed, I will no longer be able to update it in GetStream.</p>
  
  <p>Am I missing anything?</p>