title: How to append to a path with additional objects in Firebase?
body: <p>I have data structures as such:</p>
  
  <pre><code>karmadots/events = 
  
  {
    "event1": {
      "categories" : ["fun"],
      "name": "Some Title"
    }
  }
  </code></pre>
  
  <p>I want to be able to append to categories and make it so it has ["fun", "outside"]. How can I achieve this? When I update child values on the event path, the entire categories path gets reset.</p>
  
  <p>EDIT:</p>
  
  <pre><code>    @IBAction func acceptUser(sender: AnyObject) {
  
      //  eventRef = karmadots/events (above)
      var myRef = eventRef.childByAppendingPath("event1")
      var eventDataOne = [
          "categories":["fun"]
      ]
      myRef.updateChildValues(eventDataOne)
  
      // categories = ["fun"]
  
      var eventDataTwo = [
          //I want to be able to append to categories instead of overwriting
          "categories":["outside"]
      ]
      myRef.updateChildValues(eventDataTwo)
  
      // categories = ["outside"] BUT I want it to be ["fun", "outside"]
  }
  </code></pre>
  
  <p>I want to be able append to categories on my second call. </p>