add badges for node version and deps

README.md

@@ -1,4 +1,6 @@
 [![Build Status](https://travis-ci.org/peers/peerjs-server.png?branch=master)](https://travis-ci.org/peers/peerjs-server)
+![node](https://img.shields.io/node/v/peer)
+![David](https://img.shields.io/david/peers/peerjs-server)
 [![npm version](https://badge.fury.io/js/peer.svg)](https://www.npmjs.com/package/peer)
 [![Downloads](https://img.shields.io/npm/dm/peer.svg)](https://www.npmjs.com/package/peer)
 [![Docker Image Size (latest semver)](https://img.shields.io/docker/image-size/peerjs/peerjs-server)](https://hub.docker.com/r/peerjs/peerjs-server)