chain instead of single cert

nginx/sites-available/vkk.medizin.uni-halle.de.conf

@@ -9,7 +9,7 @@ server {
     set                 $base /home/app/web/;
 
     # SSL
-    ssl_certificate     /etc/nginx/ssl/vkk.medizin.uni-halle.de.crt;
+    ssl_certificate     /etc/nginx/ssl/fullchain.pem;
     ssl_certificate_key /etc/nginx/ssl/vkk.medizin.uni-halle.de.key;
 
     # security