update the script so that it stops breaking the demo

[notwaldorf]

The script hadn't been updated to the new hydrolysis ways, and stomped over the things that made the demo work in the catalog (see: https://github.com/PolymerElements/iron-icons/commit/402d0b03afce0477ecb24e75b3860c64a9b0a13e#diff-bd4da5170a66537253748f17390d0344L31)

/cc @azakus

[garlicnation]

LGTM