ISSUE #142: remove word incubator in coveralls.io in README

Descriptions of the changes in this PR:
[INFRA-14937](https://issues.apache.org/jira/browse/INFRA-14937) ticket has been solved, so update the coveralls link here.

Author: Jia Zhai <zhaijia@apache.org>

Reviewers: Sijie Guo <sijie@apache.org>

This closes #159 from zhaijack/issue_142, closes #142
diff --git a/README.md b/README.md
index 288351c..9af2f35 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 [![Build Status](https://api.travis-ci.org/apache/distributedlog.svg?branch=master)](https://travis-ci.org/apache/distributedlog)
 [![Build Status](https://builds.apache.org/buildStatus/icon?job=distributedlog-nightly-build)](https://builds.apache.org/job/distributedlog-nightly-build/)
-[![Coverage Status](https://coveralls.io/repos/github/apache/incubator-distributedlog/badge.svg?branch=master)](https://coveralls.io/github/apache/incubator-distributedlog?branch=master)
+[![Coverage Status](https://coveralls.io/repos/github/apache/distributedlog/badge.svg?branch=master)](https://coveralls.io/github/apache/distributedlog?branch=master)
 
 # Apache DistributedLog