Treemap titles are not centered when multi-line name used

[Coding-with-Adam]

Original issue reported in plotly.py #4537

In the first image, you'll find that the title parent1<br>new is aligned in the center.

In this second image, you'll see that the title appears to not be centered. In fact, only the bottom line is centered, and the top line, parent1, is left-aligned to the bottom line. Codepen.

A bug fix would allow the centering of titles that have multiple lines.