CI/BUG?: test_pct_max_many_rows crashes on travis-27.
Following Ian Fleming ("Once is happenstance. Twice is coincidence. Three times is enemy action"), here are the three most recent builds from #23582 -- which *only* changes tests -- wherein there is a single failure/crash in the `travis-27.yaml` build for `pandas/tests/series/test_rank.py::test_pct_max_many_rows`, which looks like this:

```
[...]
........................................................................ [ 87%]
..........................................................[gw0] node down: Not properly terminated
fReplacing crashed worker gw0
gw2 [39907] / gw1 [39907]. [ 87%]
........................................................................ [ 87%]
........................................................................ [ 87%]
[...]
........................................................................ [ 99%]
.....
=================================== FAILURES ===================================
_______________________ pandas/tests/series/test_rank.py _______________________
[gw0] linux2 -- Python 2.7.15 /home/travis/miniconda3/envs/pandas/bin/python
Worker 'gw0' crashed while running 'pandas/tests/series/test_rank.py::test_pct_max_many_rows'
```

https://travis-ci.org/pandas-dev/pandas/jobs/455175414
https://travis-ci.org/pandas-dev/pandas/jobs/455259318
https://travis-ci.org/pandas-dev/pandas/jobs/455642129

Interestingly, the azure 2.7 builds pass both for windows and linux. Any ideas?