Preserve version on Autoloading Guide redirect

The v4.2 and v5.0 guides are the only guides which link to
`constant_autoloading_and_reloading.html`.  However, visiting that path
in either version currently redirects to the stable version of
`autoloading_and_reloading_constants.html`, which is a Zeitwerk guide as
of Rails 6.0.

This commit preserves the guide version when redirecting.

Author: jonathanhefner

config/nginx.conf

@@ -41,7 +41,7 @@ server {
 
     rewrite /contributing_to_rails.html /contributing_to_ruby_on_rails.html permanent;
     rewrite /contribute.html /contributing_to_ruby_on_rails.html permanent;
-    rewrite /constant_autoloading_and_reloading.html /autoloading_and_reloading_constants.html permanent;
+    rewrite ^(.*)/constant_autoloading_and_reloading.html$ $1/autoloading_and_reloading_constants.html permanent;
 
     location ~ ^/v\d {
       root /home/rails/guides;