[docs] fix code typo from writing-a-component. h/t @utopiah
[docs] fix code typo from writing-a-component. h/t @utopiah

weddingdj/aframe,dmarcos/aframe,fernandojsg/aframe,darkwing/aframe,fernandojsg/aframe,RSpace/aframe,aframevr/aframe,dmarcos/aframe,jaxmolina/ar,chenzlabs/aframe,weddingdj/aframe,ngokevin/aframe,darkwing/aframe,jaxmolina/ar,mkungla/aframe,aframevr/aframe,googlecreativelab/aframe,mkungla/aframe,wizgrav/aframe,googlecreativelab/aframe,chenzlabs/aframe,ngokevin/aframe,RSpace/aframe,wizgrav/aframe