Teach apt-get not to use IPv6 addresses

Create a file in /etc/apt/apt.conf.d/ starting with 90 or higher.
Example /etc/apt/apt.conf.d/90ipv6only

Put inside the following:

Acquire::ForceIPv4 "true"; 

and the do apt-get update.

This works on Debian Jessie/Devuan Jessie.