Update Dumper.php

Hi fellows,
Due to strong popularity of Twig and of Silex I found usefull if AsseticProvider could manage Twig namespaces, you think so?

Oh, and there is not control if the method below can't find any TwigResource. Better to throw an Exception or whatever...
patch-2
conflict file removed
bad merging fixed
Merge pull request #19 from spil-giacomo/patch-2

Update Dumper.php