docs: add build badge

Author: imyelo

readme.md

@@ -1,8 +1,8 @@
 # Padoracle
 > Padding Oracle Attack with Node.js
 
+[![Build Status](https://travis-ci.org/imyelo/padoracle.svg?branch=master)](https://travis-ci.org/imyelo/padoracle)
 [![npm](https://img.shields.io/npm/v/padoracle.svg?style=flat-square)](https://www.npmjs.com/package/padoracle)
-[![npm](https://img.shields.io/npm/dw/padoracle.svg?style=flat-square)](https://www.npmjs.com/package/padoracle)
 [![license](https://img.shields.io/npm/l/padoracle.svg?style=flat-square)](./LICENSE)
 [![PRs Welcome](https://img.shields.io/badge/PRs-welcome-brightgreen.svg?style=flat-square)](http://makeapullrequest.com)