Packaging darwin build on Windows results in blocked folder (access denied)

Hi there,
I've just started using the packager, and it works pretty well. Thanks for the great work and the efforts here :)

I just have a problem with building for Mac on Windows. I use this line of code:

`D:\work\www\droplet>electron-packager ./ Droplet --platform=darwin --arch=x64 --
version=0.33.9 --out=build`

And the build was successful:

```
Packaging app for platform darwin x64 using electron v0.33.9
Wrote new app to build\Droplet-darwin-x64
```

But here comes the problem - I cannot archive or copy this build. When archiving with WinRAR, I get the following error:

```
! D:\work\www\droplet\build\Droplet-darwin-x64.rar: Cannot open D:\work\www\droplet\build\Droplet-darwin-x64\Droplet.app\Contents\Frameworks\Electron Framework.framework\Libraries
Access is denied.
! D:\work\www\droplet\build\Droplet-darwin-x64.rar: Cannot open D:\work\www\droplet\build\Droplet-darwin-x64\Droplet.app\Contents\Frameworks\Electron Framework.framework\Resources
Access is denied.
```

Followed by a 5 seconds wait time, and another like 10 errors for maybe all things in `Frameworks` folder.

I've managed to copy it through cmd, using xcopy, BUT the build was 50% larger (don't know why), and does not run on Mac: `The application “Droplet.app” can’t be opened.`

Do you have any ideas why this happens? Using Windows builds (on any arch) works like a charm! Any ideas will be appreciated!