CI: slowdown
something is happening on travis about 8 days ago. our builds took between 2 & 2.5 hrs.

2.5 hrs: https://travis-ci.org/pandas-dev/pandas/builds/241842849

now taking 3.5 hrs +, with very little changes in code.
3.5 hrs: https://travis-ci.org/pandas-dev/pandas/builds/241844274

It *seems* that the tests themselves are taking 2x longer.

any ideas?