add flake8 testing environment

.travis.yml

@@ -3,6 +3,7 @@ python:
   - "2.7"
 env:
   - TOX_ENV=docs
+  - TOX_ENV=flake8
   - TOX_ENV=py27
   - TOX_ENV=py33
   - TOX_ENV=py34

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py{27,33,34},docs
+envlist = py{27,33,34},docs,flake8
 
 [testenv]
 basepython =
@@ -27,3 +27,15 @@ deps =
 changedir = docs
 commands =
     sphinx-build -W -b html -d {envtmpdir}/doctrees . _build/html
+
+[flake8]
+application-import-names = pelican
+import-order-style = cryptography
+
+[testenv:flake8]
+basepython = python2.7
+deps =
+    flake8 <= 2.4.1
+    git+https://github.com/public/flake8-import-order@2ac7052a4e02b4a8a0125a106d87465a3b9fd688
+commands =
+    flake8 pelican