Update README image with high resolution one

Author: kunalkapadia

README.md

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 # express-es6-rest-api-starter
 Starter project for an ES6 RESTful Express API.
 
-# [![Express ES6 REST API Starter](https://cloud.githubusercontent.com/assets/4172932/12559828/4a17edca-c3bd-11e5-815c-0e24534b5715.jpg)](https://github.com/KunalKapadia/express-es6-rest-api-starter)
+# [![Express ES6 REST API Starter](https://cloud.githubusercontent.com/assets/4172932/12560357/41ba5c50-c3c0-11e5-84b4-218cef4fcbdc.jpg)](https://github.com/KunalKapadia/express-es6-rest-api-starter)
 
 ## Overview