Union bbox transforms of shapes, not bounds of shapes.

If you rotate the bounding box of a circle and take the bounding box of the rotated bounding box it's not the same as the actual union of the bounds. This corrects that oversight.

What's Changed

• Fix union_bbox() by @ptomulik in #195

New Contributors

• @ptomulik made their first contribution in #195

Full Changelog: 1.8.1...1.8.2