add black check

.travis.yml

@@ -1,21 +1,20 @@
 language: python
 sudo: false
+dist: xenial
 python:
     - 2.7
     - pypy
     - 3.4
     - 3.5
     - 3.6
-matrix:
-    include:
-        - python: "3.7"
-          dist: xenial
-          sudo: true
+    - pypy3
+    - 3.7
 install:
-    - virtualenv .
-    - bin/pip install zc.buildout
-    - bin/buildout
+    - if [ -x "$(command -v pip3)" ]; then pip3 install black; fi;
+    - pip install zc.buildout
+    - buildout
 script:
+    - if [ -x "$(command -v black)" ]; then black src setup.py; fi;
     - bin/test -v1
 notifications:
     email: false