Backup has failed. pg_dump: server version: 9.6.3; pg_dump version: 9.5.10

Dev
7

Maybe you got bit by the fact that they support: 14.04, 16.04, 17.04 and 18.04 but skipped 17.10.

In the above snipped I set do you get 17.04 packages, that in my experience work just fine.