Remove Python 2.6 on OS X from the Travis build matrix

Build times on these jobs have somehow crept up to nearly (and
occasionally surpassing) the Travis timeout (50 minutes). Additionally,
a look at the PyPI bigquery data indicates that 2.6 represents
approximately 0.4% of OS X downloads. Since this CI overhead is
causing the project significant pain for almost no gain, it's time to
eliminate it.
1 file changed