Remove empty directories from release zip
Remove empty directories from release zip

This was a regression from #6383, when nodir was removed from globby but
I accidentally removed it from direct `gulp.src` calls as well.

Reported on the forum: https://groups.google.com/d/msg/cesium-dev/709bHz4P_nQ/JMauc6bjAwAJ

josh-bernstein/cesium,geoscan/cesium,soceur/cesium,likangning93/cesium,kaktus40/cesium,YonatanKra/cesium,josh-bernstein/cesium,hodbauer/cesium,AnalyticalGraphicsInc/cesium,likangning93/cesium,AnalyticalGraphicsInc/cesium,CesiumGS/cesium,CesiumGS/cesium,geoscan/cesium,CesiumGS/cesium,likangning93/cesium,hodbauer/cesium,soceur/cesium,YonatanKra/cesium,oterral/cesium,soceur/cesium,CesiumGS/cesium,oterral/cesium,likangning93/cesium,likangning93/cesium,YonatanKra/cesium,oterral/cesium,hodbauer/cesium,progsung/cesium,CesiumGS/cesium,jasonbeverage/cesium,YonatanKra/cesium,jasonbeverage/cesium,kaktus40/cesium,progsung/cesium