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
HINSTANCE hinstance,
    shared_ptr<NotificationData> data) {
  return CreateWindowEx(WS_EX_LAYERED | WS_EX_NOACTIVATE | WS_EX_TOPMOST,
                        class_name_, nullptr, WS_POPUP, 0, 0, 0, 0, NULL, NULL,
                        hinstance, &data);
}
void DesktopNotificationController::Toast::Draw() {
  const COLORREF accent = GetAccentColor();
  COLORREF back_color;
  {
    
    
    int h = is_highlighted_ ? (0xff / 20) : 0;
    back_color = RGB(min(0xff, (GetRValue(accent) * 2 / 3) + h),
                     min(0xff, (GetGValue(accent) * 2 / 3) + h),
                     min(0xff, (GetBValue(accent) * 2 / 3) + h));
  }
  const float back_luma = (GetRValue(back_color) * 0.299f / 255) +
                          (GetGValue(back_color) * 0.587f / 255) +
                          (GetBValue(back_color) * 0.114f / 255);
  const struct {
    float r, g, b;
  } back_f = {
      GetRValue(back_color) / 255.0f,
      GetGValue(back_color) / 255.0f,
      GetBValue(back_color) / 255.0f,
  };
  COLORREF fore_color, dimmed_color;