[mediacapture-image] Replace redEye example with one exercising zoom.

miguelao has just created a new issue for 
https://github.com/w3c/mediacapture-image:

== Replace redEye example with one exercising zoom. ==
Replace example num.2 
https://w3c.github.io/mediacapture-image/#taking-a-picture-with-red-eye-reduction-supported-and-used
 with an example manipulating e.g. Zoom, that is more visual and is 
already available, while the changes in #73 are being addressed. Will 
do that quickly.

Please view or discuss this issue at 
https://github.com/w3c/mediacapture-image/issues/103 using your GitHub
 account