No SSL redirects with Spree

nginx.conf

server {
  server_name example.com;
  listen 80;
  root /var/www/my_app/public;
  passenger_enabled on;

  error_page 500 502 503 504 /500.html;
  client_max_body_size 4G;
  keepalive_timeout 10;
}

server {
  server_name example.com;
  listen 443;
  root /var/www/my_app/public;
  passenger_enabled on;

  ssl_certificate      /etc/nginx/conf.d/.ssl/example.com.crt;
  ssl_certificate_key  /etc/nginx/conf.d/.ssl/example.com.key;
  ssl on;
  error_page 500 502 503 504 /500.html;
  client_max_body_size 4G;
  keepalive_timeout 10;
}