After creating a notification and passing a tag, then subsequent notifications with the same tag don't show up for the entire lifespan of the app.

* Electron version: 1.8.1
* Operating system: Windows 7 x64

### Expected behavior

New notifications should open after the last one has closed.

### Actual behavior

Nothing happens

### How to reproduce

  $ git clone https://github.com/electron/electron-quick-start .
  $ npm install
  $ npm start

Then in the app open dev tools and paste this in the console:

    new Notification("test", { tag: "test" });

Wait for the notification to disappear and paste it again, observe nothingness.
atom/browser/notifications/win/win32_desktop_notifications/toast.cc
}
  
  {
    RECT rc = {text_offset_x, margin_.cy, close_button_rect_.left,
               toast_size_.cy};
    SelectFont(hdc_, caption_font);
    SetTextColor(hdc_, fore_color);
    DrawText(hdc_, data_->caption.data(), (UINT)data_->caption.length(), &rc,
             DT_SINGLELINE | DT_END_ELLIPSIS | DT_NOPREFIX);
  }
  
  if (!data_->body_text.empty()) {
    RECT rc = {text_offset_x, 2 * margin_.cy + tm_cap.tmAscent,
               toast_size_.cx - margin_.cx, toast_size_.cy - margin_.cy};
    SelectFont(hdc_, body_font);
    SetTextColor(hdc_, dimmed_color);
    DrawText(hdc_, data_->body_text.data(), (UINT)data_->body_text.length(),
             &rc,
             DT_LEFT | DT_WORDBREAK | DT_NOPREFIX | DT_END_ELLIPSIS |
                 DT_EDITCONTROL);
  }
  
  {
    SelectFont(hdc_, caption_font);
    SetTextColor(hdc_, is_close_hot_ ? fore_color : dimmed_color);
    ExtTextOut(hdc_, close_pos.x, close_pos.y, 0, nullptr, &close, 1, nullptr);
  }
  is_content_updated_ = true;
}
void DesktopNotificationController::Toast::Invalidate() {