Rename Riot to Element.

Riot was recently renamed to Element,
as described in this blog post:
https://element.io/blog/welcome-to-element/

This commit updates the product page for
Hosted Matrix to use the new name.
Status Job ID Name Coverage
  Build
failed #5439
build

 
Name Stage Failure
failed
build Build There has been a timeout failure or the job got stuck. Check your timeout limits or try again
No job log