change start to restart also for systemctl

I've forgotten to update the systemctl start to restart in my first commit

packaging/deb/control/postinst

@@ -7,7 +7,7 @@ set -e
 startGrafana() {
   if [ -x /bin/systemctl ]; then
     /bin/systemctl daemon-reload
-    /bin/systemctl start grafana-server
+    /bin/systemctl restart grafana-server
 	elif [ -x "/etc/init.d/grafana-server" ]; then
 		if [ -x "`which invoke-rc.d 2>/dev/null`" ]; then
 			invoke-rc.d grafana-server restart || true