[ROCKETMQ-176] Use new maven central badge with the newest release version info in README.

Author: zhouxinyu

README.md

@@ -1,5 +1,5 @@
 ## Apache RocketMQ [![Build Status](https://travis-ci.org/apache/incubator-rocketmq.svg?branch=master)](https://travis-ci.org/apache/incubator-rocketmq) [![Coverage Status](https://coveralls.io/repos/github/apache/incubator-rocketmq/badge.svg?branch=master)](https://coveralls.io/github/apache/incubator-rocketmq?branch=master)
-[![Maven Central](https://img.shields.io/badge/maven--center-stable--version-green.svg)](http://search.maven.org/#search%7Cga%7C1%7Corg.apache.rocketmq)
+[![Maven Central](https://maven-badges.herokuapp.com/maven-central/org.apache.rocketmq/rocketmq-all/badge.svg)](http://search.maven.org/#search%7Cga%7C1%7Corg.apache.rocketmq)
 [![GitHub release](https://img.shields.io/badge/release-download-orange.svg)](https://github.org/apache/rocketmqreleases)
 [![License](https://img.shields.io/badge/license-Apache%202-4EB1BA.svg)](https://www.apache.org/licenses/LICENSE-2.0.html)