[doc] geometry.md: no update lifecycle method
[doc] geometry.md: no update lifecycle method

registered custom geometries do not have an update method.
mkungla/aframe,dmarcos/aframe,googlecreativelab/aframe,jaxmolina/ar,ngokevin/aframe,weddingdj/aframe,weddingdj/aframe,ngokevin/aframe,RSpace/aframe,dmarcos/aframe,chenzlabs/aframe,googlecreativelab/aframe,darkwing/aframe,aframevr/aframe,wizgrav/aframe,chenzlabs/aframe,wizgrav/aframe,RSpace/aframe,darkwing/aframe,aframevr/aframe,jaxmolina/ar,mkungla/aframe