Fix the Real World OCaml link (#3656)

free-programming-books.md

@@ -1999,7 +1999,7 @@ Kerridge (PDF) (email address *requested*, not required)
 
 * [Developing Applications With Objective Caml](http://caml.inria.fr/pub/docs/oreilly-book/)
 * [Functional Programming in OCaml](https://www.cs.cornell.edu/courses/cs3110/2019sp/textbook/) - Michael R. Clarkson
-* [Real World OCaml](https://realworldocaml.org/v1/en/html/)
+* [Real World OCaml](https://dev.realworldocaml.org/toc.html)
 * [Think OCaml](http://greenteapress.com/thinkocaml/index.html) - Allen B. Downey and Nicholas Monje
 * [Unix System Programming in OCaml](http://ocaml.github.io/ocamlunix/) [Github Repo](https://github.com/ocaml/ocamlunix/)
 * [Using, Understanding, and Unraveling The OCaml Language: From Practice to Theory and vice versa](http://pauillac.inria.fr/~remy/cours/appsem/) - Didier Rémy