* **Electron Version:**
  * 5.0.x
* **Operating System:**
  * macOS 10.14.5

### Expected Behavior
Electron does not crash at exit.

### Actual Behavior
The notifications are sent well, i use the close() function to avoid persistence in Notification Center. 

By doing this every time I quit the application I have a message that warns me that the application did not stop properly.

### To Reproduce
```javascript
const notif = new Notification({title: title, body: body, silent: true})
notif.on('click', () => appEvent.emit('show-window'))
notif.show()
setTimeout(() => notif.close(), 10000)
```
After sending notification(s), close application (app.quit()) and the error will appear.

To no longer have the error after quitting app, i do not use the function close () but my application generates a lot of notifications and I would have preferred to handle that.

shell/browser/api/atom_api_notification.cc
v8::Local<v8::Value> val,
                     electron::NotificationAction* out) {
    gin::Dictionary dict(isolate);
    if (!ConvertFromV8(isolate, val, &dict))
      return false;
    if (!dict.Get("type", &(out->type))) {
      return false;
    }
    dict.Get("text", &(out->text));
    return true;
  }
  static v8::Local<v8::Value> ToV8(v8::Isolate* isolate,
                                   electron::NotificationAction val) {
    gin::Dictionary dict = gin::Dictionary::CreateEmpty(isolate);
    dict.Set("text", val.text);
    dict.Set("type", val.type);
    return ConvertToV8(isolate, dict);
  }
};
}  
namespace electron {
namespace api {
Notification::Notification(gin::Arguments* args) {