Sample update hook: typofix and modernization to use "git log"

Sample update hook: typofix and modernization to use "git log"

Instead of using antiquated "git-rev-parse | git-rev-list"
pipeline, it is easier to use "git-rev-list" or "git-log" these
days, as Linus points out.

While we are at it, fix the typo on variable name $newref that
should be $newrev.

Signed-off-by: Andy Parkins <andyparkins@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>