Update README.md

Author: kevinongko

README.md

@@ -4,6 +4,7 @@
 [![npm](https://img.shields.io/npm/dt/vue-numeric.svg)](https://www.npmjs.com/package/vue-numeric)
 [![npm](https://img.shields.io/npm/dm/vue-numeric.svg)](https://www.npmjs.com/package/vue-numeric)
 [![Build Status](https://travis-ci.org/kevinongko/vue-numeric.svg?branch=master)](https://travis-ci.org/kevinongko/vue-numeric)
+[![codecov](https://codecov.io/gh/kevinongko/vue-numeric/branch/master/graph/badge.svg)](https://codecov.io/gh/kevinongko/vue-numeric)
 [![npm](https://img.shields.io/npm/l/vue-numeric.svg)](http://opensource.org/licenses/MIT)
 
 Input field component to display currency value based on [Vue](https://vuejs.org/).