title: can getstream aggregation work on properties of the "object" property
body: <p>I set up the aggregation rule:</p>
  
  <pre><code>{{ object.experienceId }}
  </code></pre>
  
  <p>on a notification feed in getstream.io expecting it to aggregate based on the object.experienceId, but instead it seems to aggregate everything into one, regardless of object.experienceId.  Am I mis-understanding how aggregation works?  What could be the issue?</p>
  
  <pre><code>    var activity = {
          time: new Date(),
          verb: 'created',
          actor: { id: 1, name: 'User One' },
          object: {
              id: 2,
              experienceId: 12,
              caption: 'Moment 1',
              photo:
              { id: '314e00a2-2455-11e5-b696-feff819cdc9f',
                  mainColor: 'ff3333',
                  width: 1000,
                  height: 400 },
              createdBy: {
                  id: 1, name: 'User One'
              },
              type: 'Moment' },
          context: 'http://derbyapp.co'
      };
  
  
      notifications.addActivity(activity,
  </code></pre>