Use tox in .travis.yml.

.travis.yml

 language: python
-python:
-  - "pypy"
-  - "2.6"
-  - "2.7"
-  - "3.2"
-  - "3.3"
-  - "3.4"
-cache:
-  - $HOME/.pip-cache
-install:
-  - pip install -r requirements-dev.txt --download-cache $HOME/.pip-cache
-  - if [[ $TRAVIS_PYTHON_VERSION == '2.6' ]]; then pip install unittest2; fi
-  - pip install --allow-all-external -e .
-script: nosetests
+env:
+  - TOXENV=py26
+  - TOXENV=py27
+  - TOXENV=py33
+  - TOXENV=py34
+  - TOXENV=pypy
+  - TOXENV=pypy3
+install: pip install tox
+script: tox