update real world's haskell zh url

free-programming-books-zh.md

@@ -413,7 +413,7 @@
 ### Haskell
 
 * [Haskell 趣学指南](http://learnyoua.haskell.sg)
-* [Real World Haskell 中文版](http://rwh.readthedocs.org/en/latest/)
+* [Real World Haskell 中文版](http://cnhaskell.com/)
 
 
 ### HTML / CSS