title: CLLocationButton in UIStackView
body: <p>I am having an issue when adding <code>CLLocationButton</code> in <code>UIStackView</code>. I can add another UI elements like <code>UILabel</code>,<code>UIButton</code>,<code>UIView</code> in <code>UIStackView</code> but when adding <code>CLLocationButton</code>, it becomes invisible. Here is my code in objective-c.</p>
  <pre><code>  self.currentLocationButton = [[CLLocationButton alloc] initWithFrame:CGRectZero];
      self.currentLocationButton.icon = CLLocationButtonIconArrowFilled;
      self.currentLocationButton.label = CLLocationButtonLabelShareCurrentLocation;
      self.currentLocationButton.backgroundColor = [UIColor greenColor];
      [self.buttonStackView addSubview:self.currentLocationButton];
      [self.currentLocationButton addTarget:self action:@selector(askForLocation:) forControlEvents:UIControlEventTouchUpInside];
      [self.currentLocationButton.heightAnchor constraintEqualToConstant:70].active = YES;
  </code></pre>
  <p>How can I see <code>CLLocationButton</code> in <code>UIStackView</code>?</p>