modify service file

Change-Id: I5c29b2bee7098fc135a873e018f47c1104ec3969
diff --git a/systemd/ndncert-server.service.in b/systemd/ndncert-server.service.in
index b8b81cc..443fc44 100644
--- a/systemd/ndncert-server.service.in
+++ b/systemd/ndncert-server.service.in
@@ -1,9 +1,10 @@
 [Unit]
 Description=Certificate Management Service for NDN
-BindsTo=nfd.service
+Wants=nfd.service
 After=nfd.service
 
 [Service]
+Type=simple
 Environment=HOME=%S/ndn/ndncert
 EnvironmentFile=-@SYSCONFDIR@/default/ndncert
 ExecStart=@BINDIR@/ndncert-ca-server $FLAGS
@@ -32,4 +33,5 @@
 
 [Install]
 WantedBy=multi-user.target
-WantedBy=nfd.service
+Alias=ndncert.service
+Alias=ndncert-ca.service
\ No newline at end of file