Add linter (flake8) back

Author: prmtl

.travis.yml

@@ -32,5 +32,5 @@ matrix:
       python: 3.8-dev
       dist: xenial
       sudo: true
-    # - env: TOXENV=py36-linters
-    #   python: 3.6
+    - env: TOXENV=py36-lint
+      python: 3.6

tox.ini

@@ -1,20 +1,19 @@
 [tox]
-envlist = py27, py36, py37
+envlist = py27, py36, py37, lint
+
 
 [testenv]
-usedevelop = True
-setenv = VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/test-requirements.txt
-commands =
-    py.test -v {posargs:test/}
+commands = py.test -v {posargs:test/}
+
 
-[testenv:pep8]
-deps = hacking==0.10.1
-usedevelop = False
+[testenv:lint]
+deps =
+  flake8==3.5.0
+skip_install = True
 commands = flake8
 
+
 [flake8]
-exclude = .venv,.tox,dist,doc,*.egg,build
 show-source = true
-# H105 - author tags in files
-ignore = H105
+max-line-length = 99