update for latest caddy version

proxy_header has been deprecated

web-server/caddy/Caddyfile

@@ -14,9 +14,9 @@ https://gitlab.example.com {
     proxy / http://127.0.0.1:8181 {
         fail_timeout 300s
-        proxy_header Host {host}
-        proxy_header X-Real-IP {remote}
-        proxy_header X-Forwarded-Proto {scheme}
-        proxy_header X-Forwarded-Ssl on
+        header_upstream Host {host}
+        header_upstream X-Real-IP {remote}
+        header_upstream X-Forwarded-Proto {scheme}
+        header_upstream X-Forwarded-Ssl on
     }
 }