title: Batch update works as set operation
body: <p>I need to do a batch update with Firebase's real-time database. I have done it like so:</p>
  <p>This is working fine. But I need an update only for the 2nd operation. At this moment it works as <code>set</code> operation. Any clue?</p>
  <pre><code> const updates = {}; //batch operation
  
     // this is working fine and I need it as set operation
      updates[`groups/${this.groupId}/leads/${lead.id.toString()}`] = {
        name: lead.name,
        address: lead.address,
      };
  
      // But problem is here. I need to write it as update operation
      updates[`groups/${this.groupId}/addresses/${lead.id.toString()}`] = {
        address: lead.address,
       };
  
      return this.angularFireDatabase.object('/').update(updates);
  </code></pre>