Raw must be static.

I got the following error 

Strict warning: Non-static method Fhaculty\Graph\GraphViz::raw() should not be called statically, assuming $this from incompatible context in Fhaculty\Graph\Loader\UmlClassDiagram->createVertexClass() (line 196 of sites/all/libraries/graph/lib/Fhaculty/Graph/Loader/UmlClassDiagram.php).