fix CI and add black tests

.travis.yml

@@ -5,9 +5,7 @@ python:
   - "3.4"
   - "3.5"
   - "3.6"
-  - "pypy-5.4.1"
-
 install:
-  - travis_retry pip install tox
+  - travis_retry pip install tox-travis
 script:
-  - tox
+- tox

tox.ini

@@ -1,22 +1,34 @@
 [tox]
+skip_missing_interpreters = True
 
 [testenv]
+skip_install = True
 deps =
     pytest
     pytest-flake8
-
 commands =
     pytest --flake8
 
-[flake8]
-max-line-length = 99
-exclude = .ropeproject,.tox
-show-source = True
+[testenv:py36]
+skip_install = True
+deps =
+    black
+    pytest
+    pytest-flake8
+commands =
+    black --quiet --diff --exclude modules py3status/
+    black --quiet --diff setup.py fastentrypoints.py
+    black --quiet --diff tests/
+    pytest --flake8
 
 [pytest]
+# see .flake8 file in the black project:
+# https://github.com/ambv/black/blob/master/.flake8
 flake8-ignore =
-# line break after binary operator (2018-Aug-22)
-    W504
-
-# invalid escape sequence (2018-Aug-22)
-    W605
+    E203
+    E266
+    E501
+    W503
+    C901
+flake8-max-complexity = 18
+flake8-max-line-length = 88