allow both old and new usage when passing additional options to graphviz

Author: badiku

streamz/graph.py

@@ -131,6 +131,13 @@ def readable_graph(graph):
 def to_graphviz(graph, **graph_attr):
     import graphviz
 
+    digraph_kwargs = {'name', 'comment', 'filename', 
+                      'format', 'engine', 'encoding',
+                      'graph_attr', 'node_attr', 'edge_attr', 
+                      'body', 'strict', 'directory'}
+    if not digraph_kwargs.intersection(graph_attr):
+        graph_attr = dict(graph_attr=graph_attr)
+        
     gvz = graphviz.Digraph(**graph_attr)
     for node, attrs in graph.nodes.items():
         gvz.node(node, **attrs)