Use py36 for black

Author: chdemko

tox.ini

@@ -1,14 +1,14 @@
 [tox]
-envlist = py2,py3
+envlist = py2,py3,py36
 
 [testenv]
 deps =
-	coverage
-	py3: pylint
-	py3: black
+	py2: coverage
+	py3: coverage, pylint
+	py36: black
 commands =
     py2: python2 -W ignore -m coverage run    --source=pandoc_codeblock_include setup.py test
     py3: coverage run -a --source=pandoc_codeblock_include setup.py test
     py3: pylint pandoc_codeblock_include.py setup.py tests/test_include.py
-    py3: black --check pandoc_codeblock_include.py setup.py tests/test_include.py
+    py36: black --check pandoc_codeblock_include.py setup.py tests/test_include.py