fix hello world codepen link in docs
fix hello world codepen link in docs

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