Update "app" to "your-app" to avoid module collision with require('app')

If you name your app's folder `app/` and if you run the atom-shell from the directory above that, it will result in an error, which I believe is caused by resolving `require('app')` to your `app/` folder.

So just to avoid confusion where someone might create an app with that folder and run the atom-shell from that directory.


I wrote up some details getting atom-shell working using the grunt plugin.

- https://github.com/atom/atom-shell/issues/256#issuecomment-42464026