Fix Slack invitation link (#5217)

Setup a new Heroku app based on rauchg/slackin, using Slack legacy token from the Chart.js (chartjs.slack@...) user and reCAPTCHA from the same Google account.

README.md

@@ -1,6 +1,6 @@
 # Chart.js
 
-[![travis](https://img.shields.io/travis/chartjs/Chart.js.svg?style=flat-square&maxAge=60)](https://travis-ci.org/chartjs/Chart.js) [![coveralls](https://img.shields.io/coveralls/chartjs/Chart.js.svg?style=flat-square&maxAge=600)](https://coveralls.io/github/chartjs/Chart.js?branch=master) [![codeclimate](https://img.shields.io/codeclimate/maintainability/chartjs/Chart.js.svg?style=flat-square&maxAge=600)](https://codeclimate.com/github/chartjs/Chart.js) [![slack](https://img.shields.io/badge/slack-Chart.js-blue.svg?style=flat-square&maxAge=3600)](https://chart-js-automation.herokuapp.com/)
+[![travis](https://img.shields.io/travis/chartjs/Chart.js.svg?style=flat-square&maxAge=60)](https://travis-ci.org/chartjs/Chart.js) [![coveralls](https://img.shields.io/coveralls/chartjs/Chart.js.svg?style=flat-square&maxAge=600)](https://coveralls.io/github/chartjs/Chart.js?branch=master) [![codeclimate](https://img.shields.io/codeclimate/maintainability/chartjs/Chart.js.svg?style=flat-square&maxAge=600)](https://codeclimate.com/github/chartjs/Chart.js) [![slack](https://img.shields.io/badge/slack-chartjs-blue.svg?style=flat-square&maxAge=3600)](https://chartjs-slack.herokuapp.com/)
 
 *Simple HTML5 Charts using the canvas element* [chartjs.org](http://www.chartjs.org)
 

docs/README.md

@@ -1,6 +1,6 @@
 # Chart.js
 
-[![slack](https://img.shields.io/badge/slack-Chart.js-blue.svg?style=flat-square&maxAge=600)](https://chart-js-automation.herokuapp.com/)
+[![slack](https://img.shields.io/badge/slack-chartjs-blue.svg?style=flat-square&maxAge=3600)](https://chartjs-slack.herokuapp.com/)
 
 ## Installation
 

docs/developers/contributing.md

@@ -12,7 +12,7 @@ New contributions to the library are welcome, but we ask that you please follow
 
 # Joining the project
 
- Active committers and contributors are invited to introduce yourself and request commit access to this project. We have a very active Slack community that you can join [here](https://chart-js-automation.herokuapp.com/). If you think you can help, we'd love to have you!
+ Active committers and contributors are invited to introduce yourself and request commit access to this project. We have a very active Slack community that you can join [here](https://chartjs-slack.herokuapp.com/). If you think you can help, we'd love to have you!
 
 # Building and Testing