update book to latest edition

Author: puredanger

content/guides/getting_started.adoc

@@ -43,7 +43,7 @@ There are many ways to learn the Clojure language. This tutorial covers the basi
 
 If you'd like to work from a <<xref/../../community/books#,book>>, these are some excellent starting points:
 
-image:https://images-na.ssl-images-amazon.com/images/I/51Bvd25CstL._SL160.jpg[Programming Clojure 3rd edition,link="https://a.co/bSxW6A6",width="130"] image:https://images-na.ssl-images-amazon.com/images/I/51dqOLcPL7L._SL160.jpg[Getting Clojure,link="https://pragprog.com/titles/roclojure/getting-clojure/",width="130"] image:https://images-na.ssl-images-amazon.com/images/I/6112vbQYDLL._SL160.jpg[Clojure for the Brave and True,link="https://a.co/bsviqV7",width="130"] image:https://images-na.ssl-images-amazon.com/images/I/5122uV93jfL._SL160.jpg[Living Clojure,link="https://a.co/1m2Zt4p",width="130"]
+image:https://pragprog.com/titles/shcloj4/programming-clojure-fourth-edition/shcloj4-beta-500.jpg[Programming Clojure, 4th edition,link="https://pragprog.com/titles/shcloj4/programming-clojure-fourth-edition/",width="130"] image:https://images-na.ssl-images-amazon.com/images/I/51dqOLcPL7L._SL160.jpg[Getting Clojure,link="https://pragprog.com/titles/roclojure/getting-clojure/",width="130"] image:https://images-na.ssl-images-amazon.com/images/I/6112vbQYDLL._SL160.jpg[Clojure for the Brave and True,link="https://a.co/bsviqV7",width="130"] image:https://images-na.ssl-images-amazon.com/images/I/5122uV93jfL._SL160.jpg[Living Clojure,link="https://a.co/1m2Zt4p",width="130"]
 
 If you'd like to try some practice problems: