Add an isort job

.travis.yml

@@ -1,10 +1,10 @@
 language: python
-
 matrix:
   include:
     - env: TOXENV=docs
     - env: TOXENV=pep8
     - env: TOXENV=py3pep8
+    - env: TOXENV=isort
     - env: TOXENV=packaging
     - env: TOXENV=py27
       python: 2.7

tox.ini

@@ -1,6 +1,7 @@
 [tox]
 envlist =
-    docs, packaging, pep8, py3pep8, py27, py33, py34, py35, py36, py37, pypy
+    docs, packaging, pep8, py3pep8, isort,
+    py27, py33, py34, py35, py36, py37, pypy
 
 [testenv]
 setenv =
@@ -34,6 +35,11 @@ basepython = python3.3
 deps = flake8==3.3.0
 commands = flake8 .
 
+[testenv:isort]
+basepython = python3.3
+deps = isort==4.2.5
+commands = isort --recursive --check-only --diff pip tests
+
 [flake8]
 exclude = .tox,*.egg,build,_vendor,data
 select = E,W,F