tox -e cover fails for me on macOS. This is due to the differences in the code that is run when on Linux vs. other platforms in certbot.util and its tests. Diffing my local coverage with Travis, the only difference in lines missing test coverage is:

$ diff travis.txt local.txt
< certbot/certbot/util.py                                        238     24    90%   132-134, 210, 275-281, 318, 330-340, 347, 381-382
> certbot/certbot/util.py                                        239     34    86%   30, 132-134, 210, 275-281, 301, 305, 316-318, 330-340, 347, 367-373, 381-382
< certbot/tests/util_test.py                                     392      0   100%
> certbot/tests/util_test.py                                     375     26    93%   483-487, 492-502, 507-514, 548-550, 555-557

I think tests on master should not be failing locally for people.

While there would be other ways to fix this by adding # pragma: no cover lines or writing mocked out tests for other platforms, I personally just think dropping the minimum coverage one percentage point is fine at least for now.