Remove link to gitter room

It never took off, and I very much prefer communicating through the forum
and bug tracker.

Author: marijnh

README.md

@@ -2,7 +2,6 @@
 
 [![Build Status](https://travis-ci.org/codemirror/CodeMirror.svg)](https://travis-ci.org/codemirror/CodeMirror)
 [![NPM version](https://img.shields.io/npm/v/codemirror.svg)](https://www.npmjs.org/package/codemirror)
-[![Join the chat at https://gitter.im/codemirror/CodeMirror](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/codemirror/CodeMirror)  
 
 CodeMirror is a versatile text editor implemented in JavaScript for
 the browser. It is specialized for editing code, and comes with over