Namespaces on own line (#1712)

`namespace` declarations appear on their own line in PHP FIG examples as well as in common PHP frameworks. While not officially part of PSR-2, we should still follow this common practice of not putting `namespace` declaration on the same line as `<?php`.

- http://www.php-fig.org/psr/psr-2/
- https://github.com/laravel/laravel/blob/master/app/User.php#L1-L3
- https://github.com/symfony/filesystem/blob/master/Filesystem.php#L1-L12
- https://github.com/zendframework/zend-mail/blob/master/src/Address.php#L1-L10

src/setup.php

@@ -1,4 +1,6 @@
-<?php namespace App;
+<?php
+
+namespace App;
 
 use Roots\Sage\Template;