title: TableView not updating after deleting an entry in Firebase
body: <p>I'm working on an application that uses the realtime data from Firebase. Whenever I add an entry to the database, it is displayed on the tableView, however, when I delete something from the database (manually delete it from Firebase), it is not refreshed on the application and the tableView doesn't refresh. </p>
  
  <p>Here's my code for the refreshing and the <code>viewDidLoad()</code> and <code>viewDidAppear()</code> methods.</p>
  
  <pre><code>override func viewDidLoad() {
      super.viewDidLoad()
      dbRef = FIRDatabase.database().reference().child("post-items")
      startObservingDB()
  
      self.tableView.estimatedRowHeight = 40.0
      self.tableView.rowHeight = UITableViewAutomaticDimension
  }
  
  override func viewDidAppear(_ animated: Bool){
      super.viewDidAppear(true)
  
      startObservingDB()
  }
  
  func startObservingDB(){
  
      dbRef.observeSingleEvent(of: .value, with: { (snapshot: FIRDataSnapshot) in
          var newPost = [Post]()
  
          for post in snapshot.children{
              let postObject = Post(snapshot: post as! FIRDataSnapshot)
              newPost.append(postObject)
          }
  
          self.posts = newPost
          self.tableView.reloadData()
  
      }) { (error) in
          print(error.localizedDescription)
      }
  
  }
  </code></pre>
  
  <p>What am I missing? Or what am I doing wrong?</p>