Update unstable download url

Change-Id:If17ec8dad1de435c9a0cceef4d7a7e615bb3ead1
Reviewed-on: https://asterix-gerrit.ics.uci.edu/c/incubator-asterixdb-site/+/15343
Reviewed-by: Ian Maxon <imaxon@uci.edu>
2 files changed