fix link target

RalfJung · RalfJung · commit 74dc144774fc · 2019-08-28T10:30:46.000+02:00
diff --git a/reference/src/layout/enums.md b/reference/src/layout/enums.md
@@ -376,7 +376,7 @@ enum Enum2<T> {
 }
 ```
 
-[niche]: ../glossary.html#niche
+[niche]: ../glossary.md#niche
 
 ## Unresolved questions
 
