docs(readme): update GitPitch icon

README.md

@@ -59,7 +59,7 @@ To contribute to diagram, check out [contribution guidelines](CONTRIBUTING.md).
 
 ## Who use it?
 
-[![GitPitch](https://gitpitch.com/gpimg/logo-dark.png)](https://gitpitch.com/)
+[![GitPitch](https://gitpitch.com/gpimg/logo.png)](https://gitpitch.com/)
 
 [GitPitch](https://gitpitch.com/) is a markdown presentation service for developers. Diagrams is now integrated as [Cloud Diagram Widget](https://gitpitch.com/docs/diagram-features/cloud-diagrams/) of GitPitch, so you can use the Diagrams when to create slide decks for Tech Conferences, Meetups, and Training with GitPitch.