Use $host in nginx morty.conf template

utils/templates/etc/nginx/default.apps-available/morty.conf

@@ -3,7 +3,7 @@
 location /morty {
     proxy_pass         http://127.0.0.1:3000/;
 
-    proxy_set_header   Host             \$http_host;
+    proxy_set_header   Host             \$host;
     proxy_set_header   Connection       \$http_connection;
     proxy_set_header   X-Real-IP        \$remote_addr;
     proxy_set_header   X-Forwarded-For  \$proxy_add_x_forwarded_for;