Update downloads badge to point to graph of downloads (#1011)

README.md

@@ -9,7 +9,7 @@
 [![Linux Build Status](https://img.shields.io/travis/jakubpawlowicz/clean-css/master.svg?style=flat&label=Linux%20build)](https://travis-ci.org/jakubpawlowicz/clean-css)
 [![Windows Build status](https://img.shields.io/appveyor/ci/jakubpawlowicz/clean-css/master.svg?style=flat&label=Windows%20build)](https://ci.appveyor.com/project/jakubpawlowicz/clean-css/branch/master)
 [![Dependency Status](https://img.shields.io/david/jakubpawlowicz/clean-css.svg?style=flat)](https://david-dm.org/jakubpawlowicz/clean-css)
-[![NPM Downloads](https://img.shields.io/npm/dm/clean-css.svg)](https://www.npmjs.com/package/clean-css)
+[![NPM Downloads](https://img.shields.io/npm/dm/clean-css.svg)](https://npmcharts.com/compare/clean-css?minimal=true)
 [![Twitter](https://img.shields.io/badge/Twitter-@cleancss-blue.svg)](https://twitter.com/cleancss)
 
 clean-css is a fast and efficient CSS optimizer for [Node.js](http://nodejs.org/) platform and [any modern browser](https://jakubpawlowicz.github.io/clean-css).