fix link

Author: nikomatsakis

book/src/recursive/stack.md

@@ -73,4 +73,5 @@ detect a cycle by checking in the [search graph] to see whether G has an associa
 [`cycle`] field to true...but I get ahead of myself, read the next chapters
 to learn more about that).
 
-[search graph]: ./search_graph.md
+[search graph]: ./search_graph.md
+[`cycle`]: http://rust-lang.github.io/chalk/chalk_solve/recursive/stack/struct.StackEntry.html#structfield.cycle