docs(vulnerabilities): add snyk badge

Author: chimurai

README.md

@@ -3,6 +3,7 @@
 [![Build Status](https://img.shields.io/travis/chimurai/http-proxy-middleware/master.svg?style=flat-square)](https://travis-ci.org/chimurai/http-proxy-middleware)
 [![Coveralls](https://img.shields.io/coveralls/chimurai/http-proxy-middleware.svg?style=flat-square)](https://coveralls.io/r/chimurai/http-proxy-middleware)
 [![dependency Status](https://img.shields.io/david/chimurai/http-proxy-middleware.svg?style=flat-square)](https://david-dm.org/chimurai/http-proxy-middleware#info=dependencies)
+[![dependency Status](https://snyk.io/test/npm/http-proxy-middleware/badge.svg)](https://snyk.io/test/npm/http-proxy-middleware)
 
 Node.js proxying made simple. Configure proxy middleware with ease for [connect](https://github.com/senchalabs/connect), [express](https://github.com/strongloop/express), [browser-sync](https://github.com/BrowserSync/browser-sync) and [many more](#compatible-servers).