Enhancement: ability to set className for animated path

[nemosmithasf]

it seems inconsistent to be able to set the className of the base path, but not the animating path. Especially since ostensibly, they should be one element- so any class modifications to the base will likely need to be applied to the animating path as well (e.g. pointer events)

It seems like a 2-3 line modification, so I'd be happy to submit a PR if you're wiling to accept it.