Rework travis.yml to use native Travis CI build matrix now that 3.4 is available.

Reverted to build matrix due to fact that only one of 3.3, 3.4, pypy interpreters seemed to be available at a time.  This duplicates logic from tox.ini, but not sure we have a choice
Merge pull request #4 from chrishas35/travis-ci-updates

Rework travis.yml to use native Travis CI build matrix now that 3.4 is available.