Docs: Change PDBLoader code to SVGLoader

[apclemens]

looks like it was accidentally overwritten in commit 99c0ba5

[Mugen87]

In dev the implementation of SVGLoader has changed. The loader now returns an array of ShapePath objects than can be used to create ShapeBufferGeometrys.

https://github.com/mrdoob/three.js/blob/dev/examples/webgl_loader_svg.html

I guess it makes sense to update the docs one more time in order to regard these changes.

[mrdoob]

Merging this for the time being.

[mrdoob]

Thanks!