Work around Safari bug
Work around Safari bug

`createPropertyDescriptor`, which is one of the core functions for the
entire Entity API, triggers a bug in Safari's JavaScript engine and
causes lost of breakage in Cesium.  This one line change works around the
issue and makes all Sandcastle examples work.

emackey/cesium,kiselev-dv/cesium,denverpierce/cesium,likangning93/cesium,omh1280/cesium,geoscan/cesium,aelatgt/cesium,emackey/cesium,ggetz/cesium,jasonbeverage/cesium,esraerik/cesium,esraerik/cesium,emackey/cesium,likangning93/cesium,oterral/cesium,NaderCHASER/cesium,josh-bernstein/cesium,aelatgt/cesium,wallw-bits/cesium,likangning93/cesium,esraerik/cesium,AnimatedRNG/cesium,AnalyticalGraphicsInc/cesium,YonatanKra/cesium,denverpierce/cesium,hodbauer/cesium,omh1280/cesium,kaktus40/cesium,hodbauer/cesium,soceur/cesium,aelatgt/cesium,NaderCHASER/cesium,kiselev-dv/cesium,AnimatedRNG/cesium,aelatgt/cesium,likangning93/cesium,denverpierce/cesium,AnimatedRNG/cesium,omh1280/cesium,hodbauer/cesium,denverpierce/cesium,CesiumGS/cesium,ggetz/cesium,CesiumGS/cesium,jasonbeverage/cesium,AnimatedRNG/cesium,ggetz/cesium,wallw-bits/cesium,wallw-bits/cesium,kiselev-dv/cesium,oterral/cesium,soceur/cesium,jason-crow/cesium,esraerik/cesium,josh-bernstein/cesium,jason-crow/cesium,jason-crow/cesium,CesiumGS/cesium,wallw-bits/cesium,oterral/cesium,progsung/cesium,YonatanKra/cesium,ggetz/cesium,jason-crow/cesium,AnalyticalGraphicsInc/cesium,YonatanKra/cesium,YonatanKra/cesium,likangning93/cesium,emackey/cesium,geoscan/cesium,CesiumGS/cesium,progsung/cesium,kiselev-dv/cesium,CesiumGS/cesium,omh1280/cesium,kaktus40/cesium,soceur/cesium,NaderCHASER/cesium