Incorrect deployment descriptor in Jersey chat sample

[nmeyvis]

https://github.com/Atmosphere/atmosphere-samples/blob/master/samples/rest-chat/src/main/webapp/WEB-INF/web.xml

<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:j2ee="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">

<async-supported>true</async-supported>

async-supported is Servlet 3.0 or greater.