Update docker

Changes:

- https://github.com/docker-library/docker/commit/7b00742: Merge pull request https://github.com/docker-library/docker/pull/231 from angustrau/fix/rootlesskit-docker-proxy-absolute-path
- https://github.com/docker-library/docker/commit/a73d96e: Remove --userland-proxy-path (no longer necessary)
- https://github.com/docker-library/docker/commit/db82a88: Merge pull request https://github.com/docker-library/docker/pull/232 from docker-library/github-actions
- https://github.com/docker-library/docker/commit/66fafcf: Add initial GitHub Actions CI

library/docker

@@ -11,7 +11,7 @@ Directory: 19.03
 
 Tags: 19.03.8-dind, 19.03-dind, 19-dind, stable-dind, test-dind, dind
 Architectures: amd64, arm32v6, arm32v7, arm64v8
-GitCommit: 25c81c65fe4e971ff75e67df38e8b9970b523f6e
+GitCommit: a73d96e731e2dd5d6822c99a9af4dcbfbbedb2be
 Directory: 19.03/dind
 
 Tags: 19.03.8-dind-rootless, 19.03-dind-rootless, 19-dind-rootless, stable-dind-rootless, test-dind-rootless, dind-rootless