Fix broken link

Author: aturon

README.md

@@ -81,7 +81,7 @@ This document is broken into four parts:
   cross-cutting topic, starting with
   [Ownership and resources](ownership/README.md).
 
-* **[APIs for a changing Rust](change/README.md)**
+* **[APIs for a changing Rust](changing/README.md)**
   discusses the forward-compatibility hazards, especially those that interact
   with the pre-1.0 library stabilization process.