Update README.md

Author: leebenson

README.md

@@ -127,7 +127,7 @@ Get the latest updates by following us on Twitter: https://twitter.com/reactql
 
 # New to GraphQL? Need help?
 
-<img src="https://reactql.org/assets/ext/slack_rgb.png" alt="ReactQL" width="278" />
+<img src="https://reactql.org/assets/ext/slack_mark.png" alt="ReactQL" width="70" />
 
 [Join the ReactQL slack channel here.](https://join.slack.com/t/reactql/shared_invite/enQtMjU0MjUzNDEzNzY0LWIyY2MzOGNlYmE1ZjI5ZDZhZTI2ODdiYzM2NjczYzJhZDgxYmJmYzE1NDYzZjRkYmVmNmQ3MzM0NzM3N2M5ODM)