Update index.html

Lol, good catch

Co-authored-by: Christian Liebel <christian.liebel@thinktecture.com>

index.html

@@ -1476,7 +1476,7 @@ <h3>
               user's device via a sync service). But the above recommendations
               ask the user agent to verify that, when an application scope is
               on origin A and the manifest is on a different origin B, there is
-              a UAX9rectional relationship between the two origins.
+              a bidirectional relationship between the two origins.
             </p>
             <p>
               The first check ensures that at least some page on origin A links