Downloading http://cdn-fastly.deb.debian.org/debian/dists/stretch/InRelease...
Downloading http://cdn-fastly.deb.debian.org/debian/dists/stretch/Release...
Downloading http://cdn-fastly.deb.debian.org/debian/dists/stretch/Release.gpg...

gpgv: WARNING: multiple signatures detected.  Only the first will be checked.
gpgv:  RSA key ID 2B90D010

ERROR: unable to fetch mirror: verification of detached signature failed: exit status 2