Update docker

Changes:

- https://github.com/docker-library/docker/commit/d450514: Merge pull request https://github.com/docker-library/docker/pull/172 from infosiftr/client-key-perms
- https://github.com/docker-library/docker/commit/3068415: Widen permissions on "client/key.pem" (especially for unprivileged usage)
- https://github.com/docker-library/docker/commit/4975dca: Update to 19.03.0 GA

library/docker

@@ -11,7 +11,7 @@ Directory: 19.03
 
 Tags: 19.03.0-dind, 19.03-dind, 19-dind, stable-dind, test-dind, dind
 Architectures: amd64, arm32v6, arm32v7, arm64v8
-GitCommit: 4975dca2dd357705c5613045348402ab664ccdf0
+GitCommit: 306841553919fba3de31766c2ba44b9e2cc5e2ec
 Directory: 19.03/dind
 
 Tags: 19.03.0-git, 19.03-git, 19-git, stable-git, test-git, git
@@ -26,7 +26,7 @@ Directory: 18.09
 
 Tags: 18.09.8-dind, 18.09-dind, 18-dind
 Architectures: amd64, arm32v6, arm32v7, arm64v8
-GitCommit: 6438624ec99b859db87dcef2cc75f5a961d1903c
+GitCommit: 306841553919fba3de31766c2ba44b9e2cc5e2ec
 Directory: 18.09/dind
 
 Tags: 18.09.8-git, 18.09-git, 18-git