On Mac, position of ecliptic grid lines varies with computer's time zone

[pkgw]

At least I'm pretty sure that's what's going on. This is manifested in the test_full test giving slightly different results on different macOS machines, with the diffs showing the ecliptic coordinate axis. If you do multiple runs on your own machine with different timezone settings, the diffs change. It's been a long day so one should probably verify this before spending too much time on it.

As I recall, there's some platform inconsistency about how timezones are handled in JS datetimes that we had to work around in pywwt at some point.