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
if (success)
        return color;
    }
  }
  return GetSysColor(COLOR_ACTIVECAPTION);
}
static HBITMAP StretchBitmap(HBITMAP bitmap, unsigned width, unsigned height) {
  
  
  
  BITMAP bm;
  if (!GetObject(bitmap, sizeof(bm), &bm))
    return NULL;
  if (width == 0 || height == 0)
    return NULL;
  HBITMAP result_bitmap = NULL;
  HDC hdc_screen = GetDC(NULL);
  HBITMAP alpha_src_bitmap;
  {
    BITMAPINFOHEADER bmi = {sizeof(BITMAPINFOHEADER)};
    bmi.biWidth = bm.bmWidth;
    bmi.biHeight = bm.bmHeight;
    bmi.biPlanes = bm.bmPlanes;
    bmi.biBitCount = bm.bmBitsPixel;
    bmi.biCompression = BI_RGB;
    void* alpha_src_bits;
    alpha_src_bitmap =
        CreateDIBSection(NULL, reinterpret_cast<BITMAPINFO*>(&bmi),
                         DIB_RGB_COLORS, &alpha_src_bits, NULL, 0);
    if (alpha_src_bitmap) {