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_notification.cc
#ifndef WIN32_LEAN_AND_MEAN
#define WIN32_LEAN_AND_MEAN
#endif
#include "atom/browser/notifications/win/win32_notification.h"
#include <windows.h>
#include <string>
#include <utility>
#include <vector>
#include "third_party/skia/include/core/SkBitmap.h"
namespace atom {
void Win32Notification::Show(const NotificationOptions& options) {
  auto* presenter = static_cast<NotificationPresenterWin7*>(this->presenter());
  if (!presenter)
    return;
  HBITMAP image = NULL;
  if (!options.icon.drawsNothing()) {
    if (options.icon.colorType() == kBGRA_8888_SkColorType) {
      BITMAPINFOHEADER bmi = {sizeof(BITMAPINFOHEADER)};
      bmi.biWidth = options.icon.width();
      bmi.biHeight = -options.icon.height();