CI: test_binary_arith_ops failing in travis-38-slow
```
=========================== short test summary info ============================
FAILED pandas/tests/computation/test_eval.py::TestEvalNumexprPandas::test_binary_arith_ops
= 1 failed, 14730 passed, 11 skipped, 1 xfailed, 37 warnings in 672.01s (0:11:12) =
```

e.g. https://travis-ci.org/github/pandas-dev/pandas/jobs/737965996