update chat icon

Author: alexweissman

README.md

@@ -4,7 +4,7 @@ http://www.userfrosting.com
 
 If you simply want to show that you like this project, or want to remember it for later, you should **star**, not **fork**, this repository.  Forking is only for when you are ready to create your own copy of the code to work on.
 
-[![Join the chat at https://chat.userfrosting.com/channel/support](http://puffin.rocks/media/rocketchat/logo.png)](https://chat.userfrosting.com/channel/support)
+[![Join the chat at https://chat.userfrosting.com/channel/support](https://demo.rocket.chat/images/join-chat.svg)](https://chat.userfrosting.com/channel/support)
 
 [![Click here to lend your support to: UserFrosting: A secure, modern user management system for PHP and make a donation at pledgie.com !](https://pledgie.com/campaigns/29583.png?skin_name=chrome)](https://pledgie.com/campaigns/29583)