fix broken link

Author: lolbinarycat

src/doc/rustdoc/src/write-documentation/the-doc-attribute.md

@@ -231,7 +231,7 @@ If you want to know more about inlining rules, take a look at the
 <span id="dochidden"></span>
 
 Any item annotated with `#[doc(hidden)]` will not appear in the documentation,
-unless the [`--document-hidden-items`](unstable-features.md#document-hidden-items) flag is used.
+unless the [`--document-hidden-items`](../unstable-features.md#document-hidden-items) flag is used.
 Re-exported items where one of its ancestors has
 `#[doc(hidden)]` will be considered hidden.