Fix ordering in systemd service file

See: https://bugs.archlinux.org/task/41338

Docker-DCO-1.1-Signed-off-by: Sébastien Luttringer <seblu@seblu.net> (github: seblu)

contrib/init/systemd/docker.service

@@ -1,7 +1,7 @@
 [Unit]
 Description=Docker Application Container Engine
 Documentation=http://docs.docker.com
-After=network.target
+After=network.target docker.socket
 Requires=docker.socket
 
 [Service]