Fix broken doc link.

asio/src/doc/overview/allocation.qbk

@@ -80,10 +80,10 @@ will insert appropriate memory barriers to ensure correct memory visibility
 should an asynchronous operation need to call the allocation functions from
 different threads. (Note: If the same allocator is shared across multiple
 concurrent asynchronous operations, this can result in concurrent calls to the
-memory allocation functions. Use of a [link asio.overview.strands strand] does
-not prevent these concurrent calls, as an operation may need to allocate memory
-from outside the strand. In this case, the shared allocator is responsible for
-providing the necessary thread safety guarantees.)
+memory allocation functions. Use of a [link asio.overview.core.strands strand]
+does not prevent these concurrent calls, as an operation may need to allocate
+memory from outside the strand. In this case, the shared allocator is
+responsible for providing the necessary thread safety guarantees.)
 
 [heading See Also]