Format using black

Author: virtuald

.travis.yml

@@ -10,6 +10,16 @@ script:
 - make -C docs html
 - ./build_exe.sh
 
+jobs:
+  include:
+  - stage: format-check
+    python:
+    - "3.6"
+    install:
+    - pip install black
+    script:
+    - black --check --diff .
+
 deploy:
 - provider: pypi
   user: $PYPI_USERNAME