Enable Nginx to send Content-Dispositions on specific files

nginx.conf

server {
    listen *:80;
    server_name www.example.com;
    rewrite ^(.*) http://example.com $1 permanent;
}

server {
    listen *:80;
    server_name example.com;

    # Static directory
    location /data/  {
        autoindex on;
        alias /data/;
        expires 30d;

        if ($request_filename ~ "^.*/(.+\.zip|tgz|iso|gz)$"){
            set $fname $1;
            add_header Content-Disposition 'attachment; filename="$fname"';
        }
    }

    root /srv/www/example.com;
    access_log /srv/www/example.com/logs/access.log;
    error_log /srv/www/example.com/logs/errors.log;

    # Redirect server error pages to the static page /50x.html
    error_page  500 502 504 /50x.html;
    location = /50x.html {
        root /usr/share/nginx/www;
    }
}