TST exclude pytest versions with broken unicode doctest handling.

The issue is fixed in pytest-dev/pytest#2500

Author: kmike

tox.ini

@@ -8,7 +8,7 @@ envlist = py27, pypy, py33, py34, py35, py36
 
 [testenv]
 deps =
-    pytest
+    pytest !=3.1.1, !=3.1.2
     pytest-cov
 commands =
     py.test \