fix param for `update()`
fix param for `update()`

 Changes to be committed:
	modified:   src/overlay.js

seanich/openseadragon,openseadragon/openseadragon,LarissaSmith/openseadragon,seanich/openseadragon,openseadragon/openseadragon,LarissaSmith/openseadragon