add support for ssl_dhparams to prevent 'Logjam' attack

nginx.tmpl

@@ -105,6 +105,10 @@ server {
 	ssl_certificate /etc/nginx/certs/{{ (printf "%s.crt" $cert) }};
 	ssl_certificate_key /etc/nginx/certs/{{ (printf "%s.key" $cert) }};
 
+    {{ if (exists (printf "/etc/nginx/certs/%s.dhparams.pem" $cert)) }}
+    ssl_dhparam {{ printf "/etc/nginx/certs/%s.dhparams.pem" $cert }};
+    {{ end }}
+
 	add_header Strict-Transport-Security "max-age=31536000";
 
 	{{ if (exists (printf "/etc/nginx/vhost.d/%s" $host)) }}