Fix broken a-sky primitive (fix #3428)
Fix broken a-sky primitive (fix #3428)

dmarcos/aframe,RSpace/aframe,aframevr/aframe,mkungla/aframe,wizgrav/aframe,ngokevin/aframe,chenzlabs/aframe,mkungla/aframe,ngokevin/aframe,dmarcos/aframe,aframevr/aframe,chenzlabs/aframe,wizgrav/aframe,RSpace/aframe