modify badge from png to svg (#227)

`svg` is more beautiful and most browsers support `svg`

Author: abetomo

README.md

@@ -4,8 +4,8 @@
 
 Command line tool to locally run and deploy your node.js application to [Amazon Lambda](http://aws.amazon.com/lambda/).
 
-[![BuildStatus](https://travis-ci.org/motdotla/node-lambda.png?branch=master)](https://travis-ci.org/motdotla/node-lambda)
-[![NPM version](https://badge.fury.io/js/node-lambda.png)](http://badge.fury.io/js/node-lambda)
+[![BuildStatus](https://travis-ci.org/motdotla/node-lambda.svg?branch=master)](https://travis-ci.org/motdotla/node-lambda)
+[![NPM version](https://badge.fury.io/js/node-lambda.svg)](http://badge.fury.io/js/node-lambda)
 
 ```
 node-lambda run