Make travis use tox for test running

.travis.yml

@@ -6,7 +6,6 @@ python:
   - "2.7"
 #  - "3.2"
 install:
-  - pip install . --use-mirrors
-  - pip install unittest2 --use-mirrors
+  - pip install tox unittest2
 script:
-  - $HOME/virtualenv/python$TRAVIS_PYTHON_VERSION/bin/unit2 discover icalendar []
+  - tox -e $(echo py$TRAVIS_PYTHON_VERSION | tr -d . | sed -e 's/pypypy/pypy/')