Set X-Forwarded-Ssl to on

https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/doc/settings/nginx.md#supporting-proxied-ssl
http://stackoverflow.com/questions/16042647/whats-the-de-facto-standard-for-a-reverse-proxy-to-tell-the-backend-ssl-is-used

setup/start/nginx/appconfig.ejs

@@ -36,6 +36,7 @@ server {
     proxy_set_header   X-Forwarded-For    $remote_addr;
     proxy_set_header   X-Forwarded-Host   $host;
     proxy_set_header   X-Forwarded-Proto  https;
+    proxy_set_header   X-Forwarded-Ssl    on;
 
     # upgrade is a hop-by-hop header (http://nginx.org/en/docs/http/websocket.html)
     proxy_set_header Upgrade $http_upgrade;