Fix systemd service treatment for prosody

we can also discuss about taking it out. Since I am probably the only user of this role for prosody

acmebot/defaults/main.yml

@@ -116,7 +116,7 @@ acmebot_default_services:
   nginx-proxy: "systemctl reload nginx-proxy"
   postfix: "systemctl reload postfix"
   postgresql: "systemctl reload postgresql"
-  prosody: "systemctl restart prosody"
+  prosody: "systemctl reload prosody"
 
 # authorizations to maintain without certficates (e.g. for master/follower)
 acmebot_authorizations: {}