Merge pull request #13800 from eolamey/13799-fix-docs-url-in-systemd-service-file

Fix docs URL in systemd service file.

contrib/init/systemd/docker.service

@@ -1,6 +1,6 @@
 [Unit]
 Description=Docker Application Container Engine
-Documentation=http://docs.docker.com
+Documentation=https://docs.docker.com
 After=network.target docker.socket
 Requires=docker.socket