Test circleci with python 3.6 instead of 3.5.

Author: dukebody

.circleci/config.yml

@@ -1,12 +1,12 @@
 version: 2
 jobs:
-  test_py35:
+  test_py36:
     docker:
-      - image: circleci/python:3.5
+      - image: circleci/python:3.6
     steps:
       - checkout
       - run: pip install --user tox
-      - run: ~/.local/bin/tox -e py35
+      - run: ~/.local/bin/tox -e py36
   test_py27:
     docker:
       - image: circleci/python:2.7
@@ -19,5 +19,5 @@ workflows:
   version: 2
   build_and_test:
     jobs:
-      - test_py35
+      - test_py36
       - test_py27