title: Delete button doesn't appear in UITableViewCell
body: <p>I have got an issue with getting Delete button on Edit one clicks. The problem is being that it doesn't appear at all. My code is below and it works for swiping across a cell... Thank you in advance for the help!</p>
  
  <pre><code>#import "ViewController.h"
  
  @interface ViewController ()
  
  @property (strong) NSArray *lessons;
  
  @end
  
  static NSString *identifier = @"Cell";
  
  @implementation ViewController
  
  - (void)viewDidLoad {
      [super viewDidLoad];
  
      self.lessons = @[
                       @"Computer Science",
                       @"Math",
                       @"Chemistry"
                       ];
  
      self.tableView = [[UITableView alloc] initWithFrame:self.view.frame style:UITableViewStylePlain];
      self.tableView.dataSource = self;
      self.tableView.delegate = self;
      [self.view addSubview:self.tableView];
  
      self.navigationItem.rightBarButtonItem = self.editButtonItem;
  
      [self.tableView registerClass:UITableViewCell.class forCellReuseIdentifier:identifier];
  }
  
  #pragma mark - Table view data source
  
  - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
      return self.lessons.count;
  }
  
  - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
      UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:identifier];
  
      cell.textLabel.text = self.lessons[indexPath.row];
      cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
  
      return cell;
  }
  
  - (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath {
      return YES;
  }
  
  - (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
  
  }
  
  #pragma mark - Table view delegate
  
  - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
      [tableView deselectRowAtIndexPath:indexPath animated:YES];
  }
  
  - (UITableViewCellEditingStyle)tableView:(UITableView *)tableView editingStyleForRowAtIndexPath:(NSIndexPath *)indexPath {
      return UITableViewCellEditingStyleDelete;
  }
  
  @end
  </code></pre>
  
  <p>Once I pressed Edit button.
  <img src="https://i.stack.imgur.com/tv0mV.png" alt=""></p>
  
  <p>This appears when I swiped across the cell. 
  <img src="https://i.stack.imgur.com/8EJsb.png" alt="enter image description here"></p>