Mirrors automatically update to the current version, so the link was broken. We could link to an archive site with 8.5.0 or update the URL to 8.6.0. The latter seems better since apt-get update has to be executed anyway.
The SHA256SUM for the v8.6.0 Net Install ISO was updated from http://cdimage.debian.org/debian-cd/8.6.0/amd64/iso-cd/SHA256SUMS