Time-based APT snapshots: use http://security.debian.org/debian-security instead of http://security.debian.org/

… in debian-security/updates.erb.

I’m told the URL we currently use, while not quite deprecated (yet?), is not the canonical one.

Original created by @intrigeri on 16860 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information