Updated Java security project reference. (#363)

Previous URL is not working. So find out new Resource https://spring.io/guides/gs/securing-web/ and I have tested the resource. It looks good.

Author: savankansagra

README.md

@@ -186,7 +186,7 @@ To get started, simply fork this repo. Please refer to [CONTRIBUTING.md](CONTRIB
 - [Build an Interpreter](http://www.craftinginterpreters.com/) (Chapter 4-13 is written in Java)
 - [Build a Simple HTTP Server with Java](http://javarevisited.blogspot.com/2015/06/how-to-create-http-server-in-java-serversocket-example.html)
 - [Build an Android Flashlight App](https://www.youtube.com/watch?v=dhWL4DC7Krs) (video)
-- [Build a Spring Boot App with User Authentication](https://scotch.io/tutorials/build-a-spring-boot-app-with-user-authentication)
+- [Build a Spring Boot App with User Authentication](https://spring.io/guides/gs/securing-web/)
 
 ## JavaScript: