Add flake8 testing to travis

Follows cookiecutter update in pytest-dev/cookiecutter-pytest-plugin@b327eac

Signed-off-by: Mike Fiedler <[email protected]>

.travis.yml

@@ -2,14 +2,21 @@
 
 sudo: false
 language: python
-python:
- - "2.7"
- - "pypy"
+
+matrix:
+ include:
+ - python: 2.7
+ env: TOX_ENV=py27
+ - python: pypy
+ env: TOX_ENV=pypy
+ - python: 3.6
+ env: TOX_ENV=flake8
 
 install:
  - pip install tox
- - "TOX_ENV=${TRAVIS_PYTHON_VERSION/[0-9].[0-9]/py${TRAVIS_PYTHON_VERSION/.}}"
-script: tox -e $TOX_ENV
+
+script:
+ - tox -e $TOX_ENV
 
 before_cache:
  - rm -rf $HOME/.cache/pip/log