Updating TravisCI to run against latest Django versions (1.3.7/1.4.10/1.5.5/1.6)

1.2 hasn't been supported in quite some time so I removed tests there (willing to add them back of course), 1.3/1.4/1.5 needed the latest point releases and 1.6 needed to be added to the mix.

Worth looking into adding 2.6 testing as well.