Remove slack from documentation (#1417)

* Update README.md

* Update README.md

* Update README.md

README.md

@@ -6,13 +6,11 @@
 [![NPM monthly downloads](https://img.shields.io/npm/dm/react-virtualized.svg?style=flat)](https://npmcharts.com/compare/react-virtualized?minimal=true)
 [![CircleCI](https://circleci.com/gh/bvaughn/react-virtualized/tree/master.svg?style=svg)](https://circleci.com/gh/bvaughn/react-virtualized/tree/master)
 [![Codecov badge](https://img.shields.io/codecov/c/github/bvaughn/react-virtualized/master.svg)](https://codecov.io/github/bvaughn/react-virtualized)
-[![Slack chat](https://react-virtualized.now.sh/badge.svg)](https://react-virtualized.now.sh)
 [![OpenCollective](https://opencollective.com/react-virtualized/backers/badge.svg)](#backers)
 [![OpenCollective](https://opencollective.com/react-virtualized/sponsors/badge.svg)](#sponsors)
 
 React components for efficiently rendering large lists and tabular data.
 Check out [the demo](https://bvaughn.github.io/react-virtualized/) for some examples.
-Join the official Slack chat at [react-virtualized.now.sh](https://react-virtualized.now.sh/).
 
 ### Sponsors
 The following wonderful companies have sponsored react-virtualized: