Merge pull request #1028 from python-hyper/requires-io-master

[requires.io] dependency update on master branch

Author: Lukasa

tox.ini

@@ -40,7 +40,7 @@ commands =
 
 [testenv:graphs]
 basepython=python2.7
-deps = graphviz==0.8
+deps = graphviz==0.8.1
 commands =
     python visualizer/visualize.py -i docs/source/_static