Line breaks in axis titles of scatter3d

[cpsievert]

Originally reported in plotly/plotly.R#1334

Minimal example -- https://codepen.io/cpsievert/pen/ZqgzEy

[etpinard]

Essentially a duplicate of #2551

[cpsievert]

I figured you were aware, but couldn't find a relevant issue -- thanks and feel free to close!