TravisCI: Pandas version advanced (Jan 2021) numpy is now incompatible
This turned out to be a problem with pip determining the correct dependency: for some reason it thought that the pandas requirement was for numpy&gt;=1.15
The error message
ERROR: pandas 1.2.0 has requirement numpy&gt;=1.16.5 ...

was coming from pandas itself (upon import).
The fix is to upgrade to a newer version of pip (inside the script running on travisCI).  The newer version of pip is able to corrently detect that pandas needs a newer version of numpy.
Just put pip install --upgrade pip near the top of the script.
Not sure why TravisCI doesn't just use the latest pip by default.
Reference: https://travis-ci.community/t/11214