Use relative image instead of absolute

README.md

@@ -3,7 +3,7 @@ Learn Javascript
 
 This book will teach you the basics of programming and Javascript. Whether you are an experienced programmer or not, this book is intended for everyone who wishes to learn the JavaScript programming language.
 
-[![Screen](https://raw.github.com/GitbookIO/javascript/master/assets/intro.png)](https://raw.github.com/GitbookIO/javascript/master/assets/intro.png)
+[![Screen](./intro.png)](./intro.png)
 
 JavaScript (*JS for short*) is the programming language that enables web pages to respond to user interaction beyond the basic level. It was created in 1995, and is today one of the most famous and used programming languages.