Readme: remove Gemnasium badge, use SVG for npm badge

Readme.md

@@ -2,9 +2,7 @@
 ## Canvas graphics API backed by Cairo
 
 [![Build Status](https://travis-ci.org/Automattic/node-canvas.svg?branch=master)](https://travis-ci.org/Automattic/node-canvas)
-[![NPM version](https://badge.fury.io/js/canvas.png)](http://badge.fury.io/js/canvas)
-[![Dependency Status](https://gemnasium.com/LearnBoost/node-canvas.png)](https://gemnasium.com/LearnBoost/node-canvas)
-
+[![NPM version](https://badge.fury.io/js/canvas.svg)](http://badge.fury.io/js/canvas)
 
   node-canvas is a [Cairo](http://cairographics.org/) backed Canvas implementation for [NodeJS](http://nodejs.org).