Separate flake8 check from test and update travis setting

Author: miyakogi

.travis.yml

@@ -1,4 +1,5 @@
 language: python
+dist: xenial
 
 matrix:
   include:
@@ -9,9 +10,9 @@ matrix:
     - python: 3.5
       env: TOXENV=py
     - python: 3.6
-      env: TOXENV=py,sphinx-dev,codecov
-    - python: 3.7-dev
       env: TOXENV=py
+    - python: 3.7
+      env: TOXENV=py,flake8,sphinx-dev,codecov
     - python: pypy
       env: TOXENV=py
     - python: pypy3

tox.ini

@@ -1,13 +1,12 @@
 [tox]
-envlist = py{27,34,35,36,37,py,py3},sphinx-dev
+envlist = py{27,34,35,36,37,py,py3},sphinx-dev,flake8
 
 [testenv]
 whitelist_externals =
   make
 deps =
   -rrequirements-test.txt
 commands =
-  flake8 m2r.py setup.py tests
   coverage run -m unittest discover tests
   coverage run -a -m sphinx -b html -d docs/_build/toctree -E -W -n -j auto -q docs docs/_build/html
   coverage report
@@ -21,6 +20,12 @@ commands =
   sphinx-build -b html -d docs/_build/toctree -E -W -n -j auto docs docs/_build/html
   make clean
 
+[testenv:flake8]
+deps =
+  flake8
+commands =
+  flake8 m2r.py setup.py tests
+
 [testenv:codecov]
 passenv = CI TRAVIS TRAVIS_*
 deps = codecov