clean Readme

cleaning gitter link as it goes to UK channel.

Author: Tanya Butenko

README.md

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 <img src="https://github.com/node-girls/workshop-cms/blob/master/readme-images/logo.png?raw=true">
 
-[![Join the chat at https://gitter.im/node-girls/express-workshop-complete](https://badges.gitter.im/node-girls/express-workshop-complete.svg)](https://gitter.im/node-girls/express-workshop-complete?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
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 # Express Workshop
 
 ## What is this?