Support pandas >= 1.1.0

[wfvining]

Pandas seems to have ironed out the .groupby().rolling() bugs that were introduced in version 1.1.0. Unfortunately, while the two obvious bugs that were initially holding up this change have been fixed, the behavior seems to have changed. In particular these two tests fail at pandas 1.1.3:

• tests/features/test_daytime.py::test_daytime_split_day
• tests/features/test_daytime.py::test_daytime_daylight_savings

The output for both classifies some data that is obviously daytime as night. Might still be a pandas bug, but I'm not sure at this point.

[wfvining]

rolling().groupby() in daytime._rolling_by_minute() results in strange gaps near the end of the series. I think this comes up for test_daytime_split_day but not other tests because the gaps are during the night-time periods for the other tests (and comparison with NaN is always False).

[wfvining]

Pandas 1.1.x is apparently still suffering from bugs in .groupby().rolling()