Merge pull request #53 from caicancai/link

fix: fix broken link

README.md

@@ -60,7 +60,7 @@ _Given the fact that work on ANTLR 5 is at a very early stage, there is currentl
 
 Programmers run into parsing problems all the time. Whether it’s a data format like JSON, a network protocol like SMTP, a server configuration file for Apache, a PostScript/PDF file, or a simple spreadsheet macro language—ANTLR v4 and this book will demystify the process. ANTLR v4 has been rewritten from scratch to make it easier than ever to build parsers and the language applications built on top. This completely rewritten new edition of the bestselling Definitive ANTLR Reference shows you how to take advantage of these new features.
 
-You can buy the book [The Definitive ANTLR 4 Reference](http://amzn.com/1934356999) at amazon or an [electronic version at the publisher's site](https://pragprog.com/book/tpantlr2/the-definitive-antlr-4-reference).
+You can buy the book [The Definitive ANTLR 4 Reference](http://amzn.com/dp/1934356999) at amazon or an [electronic version at the publisher's site](https://pragprog.com/book/tpantlr2/the-definitive-antlr-4-reference).
 
 You will find the [Book source code](http://pragprog.com/titles/tpantlr2/source_code) useful.