URL fix

free-programming-books.md

@@ -872,7 +872,7 @@
 * [Haskell web Programming](http://yannesposito.com/Scratch/fr/blog/Yesod-tutorial-for-newbies/) (Yesod tutorial)
 * [Learn Haskell Fast and Hard](http://yannesposito.com/Scratch/en/blog/Haskell-the-Hard-Way)
 * [Learn You a Haskell for Great Good](http://learnyouahaskell.com/) - Miran Lipovaca
-* [Natural Language Processing for the Working Programmer](http://nlpwp.org/book/index.xhtml)
+* [Natural Language Processing for the Working Programmer](http://nlpwp.org/book/)
 * [Parallel and Concurrent Programming in Haskell](http://chimera.labs.oreilly.com/books/1230000000929/index.html) -  Simon Marlow
 * [Real World Haskell](http://book.realworldhaskell.org/)
 * [Speeding Through Haskell](http://www.sthaskell.com/)