Not deleting attributes.className.

[saboya]

Hi. I came across an issue that, if I use className, when the preact components re-renders, the class attributes in my elements are lost. If I use "class", everything just works. I realize that preact recommends class over className, but since className was supposed to work as well (at least according to https://github.com/developit/preact/issues/103), I'd consider this a bug.

This is a simple change, but I imagine this code is here for a reason.

Thanks in advance!