Added Ubuntu 20.04

Author: radarhere

.github/workflows/test-docker.yml

@@ -14,6 +14,7 @@ jobs:
           arch,
           ubuntu-16.04-xenial-amd64,
           ubuntu-18.04-bionic-amd64,
+          ubuntu-20.04-focal-amd64,
           debian-9-stretch-x86,
           debian-10-buster-x86,
           centos-6-amd64,