updated link

free-programming-books.md

@@ -1376,7 +1376,7 @@
 * [Crockford's JavaScript](http://www.crockford.com/javascript/) - Douglas Crockford
 * [Dev Docs](http://devdocs.io)
 * [Developing Backbone.js Applications](http://addyosmani.github.io/backbone-fundamentals/) - Addy Osmani
-* [Directory of free Javascript ebooks](http://jsbooks.revolunet.com/)
+* [Directory of free Javascript ebooks](http://jsbooks.revolunet.com)
 * [Eloquent JavaScript 2nd edition](http://eloquentjavascript.net) - Marijn Haverbeke
 * [Exploring ES6](http://exploringjs.com/es6/) - Dr. Axel Rauschmayer
 * [Google JavaScript Style Guide](https://google.github.io/styleguide/javascriptguide.xml)