Update systemd service file with suggestions from @seblu

contrib/init/systemd/docker.service

@@ -1,11 +1,9 @@
 [Unit]
 Description=Docker Application Container Engine 
 Documentation=http://docs.docker.io
-Requires=network.target
-After=multi-user.target
+After=network.target
 
 [Service]
-Type=simple
 ExecStartPre=/bin/mount --make-rprivate /
 ExecStart=/usr/bin/docker -d