fixed Anahkiasen/rocketeer#35

Hello Anahkiasen.

I'm sorry for my bad english.
This is my first PullRequest.

I solved Anahkiasen/rocketeer#35 in my environment.
php 5.5.3
Laravel 4.0.7
rocketeer 0.7.0

I think this problem caused by below line.
https://github.com/Anahkiasen/rocketeer/blob/master/src/Rocketeer/Rocketeer.php#L214

```php
if (isset($app[$folder])) {...}
```

In actual laravel apps are `isset($app[$folder])` returns false ($folder=path.storage, path.public... etc).
But, `var_dump($app[$folder])` returns valid paths! (This is very magically for me.)

It is because of actual apps registers paths in `bootstrap/start.php`. [original](https://github.com/laravel/laravel/blob/master/bootstrap/start.php#L46)

This file call `Illuminate\Foundation\Application::bindInstallPaths()` method. 
`bindInstallPaths()` call `Illuminate\Container\Container::instance()` method.
Does not directly assignment like `$app['path.base'] = '...'`.

Please check below classes and methods.

```php
Illuminate\Container\Container::instance()
Illuminate\Container\Container::offsetExists()
Illuminate\Container\Container::offsetGet()
Illuminate\Foundation\Application::bindInstallPaths()
```

cheer!