[ISSUE #1859] add codecov report for unit tests.

[ISSUE #1859] add codecov report for tests.

.travis.yml

@@ -33,3 +33,4 @@ script:
 after_success:
   - mvn clean install -Pit-test
   - mvn sonar:sonar -Psonar-apache
+  - bash <(curl -s https://codecov.io/bash) || echo 'Codecov failed to upload'

README.md

 ## Apache RocketMQ 
 [![Build Status](https://travis-ci.org/apache/rocketmq.svg?branch=master)](https://travis-ci.org/apache/rocketmq) [![Coverage Status](https://coveralls.io/repos/github/apache/rocketmq/badge.svg?branch=master)](https://coveralls.io/github/apache/rocketmq?branch=master)
+[![CodeCov](https://codecov.io/gh/apache/rocketmq/branch/master/graph/badge.svg)](https://codecov.io/gh/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://rocketmq.apache.org/dowloading/releases)
 [![License](https://img.shields.io/badge/license-Apache%202-4EB1BA.svg)](https://www.apache.org/licenses/LICENSE-2.0.html)

pom.xml

@@ -280,7 +280,7 @@
             <plugin>
                 <groupId>org.jacoco</groupId>
                 <artifactId>jacoco-maven-plugin</artifactId>
-                <version>0.7.8</version>
+                <version>0.8.5</version>
                 <executions>
                     <execution>
                         <id>default-prepare-agent</id>