docs(readme): link download badge to npm-stats.com

README.md

@@ -2,7 +2,7 @@
 
 [![License](https://img.shields.io/npm/l/axe-core.svg)](LICENSE)
 [![Version](https://img.shields.io/npm/v/axe-core.svg)](https://www.npmjs.com/package/axe-core)
-[![Total npm downloads](https://img.shields.io/npm/dt/axe-core.svg)](https://www.npmjs.com/package/axe-core)
+[![Total npm downloads](https://img.shields.io/npm/dt/axe-core.svg)](https://npm-stat.com/charts.html?package=axe-core&from=2017-01-01)
 [![Commits](https://img.shields.io/github/commit-activity/y/dequelabs/axe-core.svg)](https://github.com/dequelabs/axe-core/commits/develop)
 [![GitHub contributors](https://img.shields.io/github/contributors/dequelabs/axe-core.svg)](https://github.com/dequelabs/axe-core/graphs/contributors)
 [![Join our Slack chat](https://img.shields.io/badge/slack-chat-purple.svg?logo=slack)](https://accessibility.deque.com/axe-community)