reduce cache time to 1 hours so future docs releases update the cloudfront caches faster

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)

This should mean publishing to docs.docker.io updates the caches faster (atm, its somewhere in the 24 hours default max-age)

@jamtur01 @ostezer