Font loader, native: FontFaceSet interface on early implementations had ready as a function instead of an attribute This fixes that by supporting both types of invocation
Font loader, native: FontFaceSet interface on early implementations had ready as a function instead of an attribute
This fixes that by supporting both types of invocation

ravn-no/readium-shared-js,readium/readium-shared-js,readium/readium-shared-js,NYPL-Simplified/readium-shared-js,kivuto/readium-shared-js,NYPL/readium-shared-js,kivuto/readium-shared-js,JoMedia/readium-shared-js,ravn-no/readium-shared-js,NYPL/readium-shared-js,NYPL-Simplified/readium-shared-js