Replace "Learn Lisp the Hard Way" dead link (#2206)

free-programming-books.md

@@ -1460,7 +1460,7 @@ For resources on Angular, Backbone, D3, Dojo, Ember, Express, jQuery, Knockout,
 * [Common Lisp the Language, 2nd Edition](http://www.cs.cmu.edu/Groups/AI/html/cltl/mirrors.html)
 * [Google's Common Lisp Style Guide](https://google.github.io/styleguide/lispguide.xml)
 * [Interpreting LISP](http://www.civilized.com/files/lispbook.pdf) - Gary D. Knott (PDF)
-* [Learn Lisp The Hard Way](http://learnlispthehardway.org/book/) - Colin J.E. Lupton
+* [Learn Lisp The Hard Way](https://github.com/LispTO/llthw) - Colin J.E. Lupton
 * [Let Over Lambda - 50 Years of Lisp](http://letoverlambda.com/index.cl/) - D. Hoyte
 * [Lisp Hackers: Interviews with 100x More Productive Programmers](https://leanpub.com/lisphackers) - Vsevolod Dyomkin
 * [Lisp Koans](https://github.com/google/lisp-koans)