Only run travis tests with py2.6, py3.3.

It is more efficient to run only one test for Python 2.x and one for
Python 3.x. The full set of tests, including all supported versions
listed in `setup.py` should be run locally at least before
releases. Then we also do coverage tests, pep8 and pyflakes.

The 'run diceware' test should remain until we have some other
regression test for bug #1.

.travis.yml

@@ -2,7 +2,6 @@ language: python
 python:
   - "2.7"
   - "3.3"
-  - "3.4"
 before_install:
   - sudo apt-get update -qq
   # Workaround for a permissions issue with Travis virtual machine images