Add branch to coveralls badge

Author: Michaela Robosova

README.md

@@ -1,4 +1,4 @@
-# vue-tree-navigation [![Version](https://img.shields.io/npm/v/vue-tree-navigation.svg)](https://www.npmjs.com/package/vue-tree-navigation) [![Coverage](https://coveralls.io/repos/github/MisRob/vue-tree-navigation/badge.svg)](https://coveralls.io/github/MisRob/vue-tree-navigation) [![License](https://img.shields.io/npm/l/vue-tree-navigation.svg)](https://www.npmjs.com/package/vue-tree-navigation)
+# vue-tree-navigation [![Version](https://img.shields.io/npm/v/vue-tree-navigation.svg)](https://www.npmjs.com/package/vue-tree-navigation) [![Coverage Status](https://coveralls.io/repos/github/MisRob/vue-tree-navigation/badge.svg?branch=master)](https://coveralls.io/github/MisRob/vue-tree-navigation?branch=master) [![License](https://img.shields.io/npm/l/vue-tree-navigation.svg)](https://www.npmjs.com/package/vue-tree-navigation)
 
 > Vue.js 2 tree navigation with vue-router support