Change logo in README

Author: pkopac

README.md

@@ -1,5 +1,5 @@
 <p align='center'>
-<a href='https://chartmogul.com'><img width='200' src='https://chartmogul.com/assets/img/logo.png'></a>
+<a href='https://chartmogul.com'><img width='200' src='https://user-images.githubusercontent.com/5329361/42206299-021e4184-7ea7-11e8-8160-8ecd5d9948b8.png'></a>
 </p>
 
 <h3 align='center'>Official ChartMogul API Python Client</h3>