Improved build matrix.

Added Python 3.4, PyPy and PyPy 3 to the build matrix.
Added Django 1.6 and 1.7 to the build matrix.
pip deprecated --use-mirrors. Instead we should use travis_retry in order to avoid failing the build due to network errors.
The build should fast finish since the matrix is large.
Fixed syntax error.
I probably shouldn't be doing this after 12 hours of work. The build will now run.
travis is case sensitive. Builds will now be excluded correctly.
Merge pull request #5 from thedrow/patch-1

Improved build matrix