coverity check enabled in README.md. .travis.yml should be updated

README.md

@@ -3,6 +3,7 @@
 [![codebeat badge](https://codebeat.co/badges/7338b3d9-520f-429b-ba55-16aec78615d1)](https://codebeat.co/projects/github-com-tamada-9rules)
 [![Gitter](https://badges.gitter.im/9rules/Lobby.svg)](https://gitter.im/9rules/Lobby?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
 [![Quality Gate](https://sonarqube.com/api/badges/gate?key=com.github:9rules)](https://sonarqube.com/dashboard/index/com.github:9rules)
+[![Coverity Scan Build Status](https://scan.coverity.com/projects/11932/badge.svg)](https://scan.coverity.com/projects/tamada-9rules)
 [![License](https://img.shields.io/badge/license-Apache%202.0-blue.svg?style=flat)](https://github.com/tamada/9rules/blob/master/LICENSE)
 [![badge](https://img.shields.io/badge/technical%20debt-visualizing-orange.svg)](http://rocat.naist.jp/heizo/9rules.html)