Update links to repo in 404.html

Now that the repo has been moved from freerange to rubycentral.

Author: chrisroos

404.html

@@ -45,9 +45,9 @@
     <h1>404 - Page not found</h1>
     <p>
       You've followed a link to an old rubyforge.org URL that we don't know what to do with.
-      If you know where it should go please <a href="https://github.com/freerange/rubyforge-redirects/issues/new">open an issue</a> including the URL of this page and the new URL of this project.
-      See the <a href="https://github.com/freerange/rubyforge-redirects/blob/main/README.md">project README</a> for more information.
+      If you know where it should go please <a href="https://github.com/rubycentral/rubyforge-redirects/issues/new">open an issue</a> including the URL of this page and the new URL of this project.
+      See the <a href="https://github.com/rubycentral/rubyforge-redirects/blob/main/README.md">project README</a> for more information.
       Thank you!
     </p>
   </body>
-</html>
+</html>