update pylint to 1.8

Author: rob

tox.ini

@@ -56,7 +56,7 @@ commands =
 deps =
     flake8
     # Needed to support Python 3.6
-    pylint >= 1.7.0
+    pylint >= 1.8.0
     # This probably breaks on Windows. See
     # <https://github.com/tox-dev/tox/issues/384>.
     -rtest/requirements.txt