Fixed camera rig typo in a-camera.md
Fixed camera rig typo in a-camera.md

Changed `id="#rig"` to `id="rig"` in camera documentation.
ngokevin/aframe,chenzlabs/aframe,aframevr/aframe,chenzlabs/aframe,aframevr/aframe,dmarcos/aframe,dmarcos/aframe,ngokevin/aframe