Inverted Y axis with zero: true

[yurivish]

If all values are the same, then the Y axis appears upside-down.

Example: https://observablehq.com/@yurivish/upside-down-y-axis

If at least one value differs from the rest, then the Y axis appears right-side-up:

[mbostock]

Heh! Good one. We will investigate.

[aimerie]

I'm experiencing this as well. I'm glad to see there is an open bug already! Any idea if this will make the next release?