Update sphere.js

I ran into a problem trying to use sphere.js to display a pano with GPano tags created by exiftool.  I found the problem was a conflict between the getAttr function (which expects GPano:FullPanoWidthPixels="3000") and the tags created by exiftool (which are the format <GPano:FullPanoWidthPixels>3000</GPano:FullPanoWidthPixels>.