Black in travis ci (keon#551)

* Add black in before_script of travis ci.

* Black reformatting of the repo.

* Remove python 3.5 from .travis.yml to support black

* Revert "Black reformatting of the repo."

This reverts commit ea0b370.

* Add black or true not to make every ci fail from this PR.

Author: laurent-pck

Diff for: .travis.yml

@@ -6,15 +6,15 @@ cache:
     - $HOME/.cache/pip
 matrix:
     include:
-        - python: 3.5
-          env: TOX_ENV=py35
         - python: 3.6
           env: TOX_ENV=py36
         - python: 3.7
           env: TOX_ENV=py37
 install:
     - pip install -r test_requirements.txt
 before_script:
+    # run black to check if some files would need reformatting
+    - black --check . || true
     # stop the build if there are Python syntax errors or undefined names
     - flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
     # exit-zero treats all errors as warnings.  The GitHub editor is 127 chars wide

Diff for: test_requirements.txt

@@ -4,3 +4,4 @@ coverage
 nose
 pytest
 tox
+black