Upgrade to Docker 19.03.8 in CI

See gh-20756

Author: spring-builds

ci/images/get-docker-url.sh

@@ -1,5 +1,5 @@
 #!/bin/bash
 set -e
 
-version="19.03.7"
+version="19.03.8"
 echo "https://download.docker.com/linux/static/stable/x86_64/docker-$version.tgz";