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
#ifndef NOMINMAX
#define NOMINMAX
#endif
#include "atom/browser/notifications/win/win32_desktop_notifications/toast.h"
#include <combaseapi.h>
#include <UIAutomation.h>
#include <uxtheme.h>
#include <windowsx.h>
#include <algorithm>
#include <cmath>
#include <memory>
#include "atom/browser/notifications/win/win32_desktop_notifications/common.h"
#include "atom/browser/notifications/win/win32_desktop_notifications/toast_uia.h"
#include "base/logging.h"
#pragma comment(lib, "msimg32.lib")
#pragma comment(lib, "uxtheme.lib")
using std::min;
using std::shared_ptr;
namespace atom {
static COLORREF GetAccentColor() {