Fix broken redirects

Author: Perksey

eng/build/Build.Website.cs

@@ -249,7 +249,7 @@ void CreateRedirectsFromOldWebsiteUrlsToNewWebsiteUrls(AbsolutePath basePath)
 
             File.WriteAllText(
                 dir.Parent / $"{dir.Name}.html",
-                GetRedirect(dir.GetRelativePathTo(basePath).ToString().Replace('\\', '/'))
+                GetRedirect(basePath.GetRelativePathTo(dir).ToString().Replace('\\', '/'))
             );
         }