Boxplots don't work in Safari

[fedarko]

As encountered by @justinshaffer (thanks!) -- the sample plot shows up fine even with a categorical axis and the samples are dots, etc., but as soon as you check the Use boxplots for categorical data? box the plot disappears.

This turned out to be a Safari issue -- switching browsers fixed the problem.

It looks like this is caused by vega/vega-lite#5197. Updating the version of Vega* (#216) should fix this problem, but in the meantime I'd advise users to just stick to Firefox or Chrome.