Set up with tox-travis

This means we don't need to specify the Tox environments in two places anymore.

Author: kevin-brown

.travis.yml

@@ -1,22 +1,13 @@
 language: python
 
 install:
-  - pip install tox coveralls
+  - pip install tox tox-travis coveralls
 matrix:
   include:
     - python: 2.7
-      env:
-          - ENV=docs
-    - python: 2.7
-      env:
-          - ENV=py27-django111
     - python: 3.5
-      env:
-          - ENV=py35-django111,py35-django20,py35-django21
     - python: 3.6
-      env:
-          - ENV=py36-django111,py36-django20,py36-django21
 script:
-  - tox -e $ENV
+  - tox
 after_success:
   - coveralls

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 envlist=
-    docs,
+    py27-docs,
     py27-django{111},
     py35-django{111,20,21},
     py36-django{111,20,21},
@@ -22,8 +22,7 @@ deps =
 commands =
     pytest --flake8 --cov=oidc_provider {posargs}
 
-[testenv:docs]
-basepython = python2.7
+[testenv:py27-docs]
 changedir = docs
 whitelist_externals =
     mkdir