undefined type 'database seeders db'
There are several ways for accessing Facade.
'DB' is alias of 'Illuminate\Support\Facades\DB', .. check in config/app.php
hence \DB means '\Illuminate\Support\Facades\DB' - fully qualified name space.
Laravel 5 uses psr-4 class loading where you need fully qualified class names.
see .. http://www.php-fig.org/psr/psr-4/ hence first '' means it starts
searching from root namespace- and includes vendor packages.
If you remove '' then it searches in your own package and didn't get
Illuminate\Support\Facades\DB.