[readme] Add branch to Coveralls URI

Author: Maks3w

README.md

@@ -1,7 +1,7 @@
 # zend-authentication
 
 [![Build Status](https://secure.travis-ci.org/zendframework/zend-authentication.svg?branch=master)](https://secure.travis-ci.org/zendframework/zend-authentication)
-[![Coverage Status](https://coveralls.io/repos/zendframework/zend-authentication/badge.svg?branch=master)](https://coveralls.io/r/zendframework/zend-authentication)
+[![Coverage Status](https://coveralls.io/repos/zendframework/zend-authentication/badge.svg?branch=master)](https://coveralls.io/r/zendframework/zend-authentication?branch=master)
 
 The `Zend\Authentication` component provides an API for authentication and
 includes concrete authentication adapters for common use case scenarios.