Readme: Swapped codeclimate reference for custom phpmetrics

Author: ssddanbrown

readme.md

@@ -5,7 +5,7 @@
 [![Crowdin](https://badges.crowdin.net/bookstack/localized.svg)](https://crowdin.com/project/bookstack)
 [![Build Status](https://github.com/BookStackApp/BookStack/workflows/test-php/badge.svg)](https://github.com/BookStackApp/BookStack/actions)
 [![Lint Status](https://github.com/BookStackApp/BookStack/workflows/lint-php/badge.svg)](https://github.com/BookStackApp/BookStack/actions)
-[![Maintainability](https://api.codeclimate.com/v1/badges/5551731994dd22fa1f4f/maintainability)](https://codeclimate.com/github/BookStackApp/BookStack/maintainability)
+[![php-metrics](https://img.shields.io/static/v1?label=Metrics&message=php&color=4F5B93)](https://source.bookstackapp.com/php-stats/index.html)
 <br>
 [![Alternate Source](https://img.shields.io/static/v1?label=Alt+Source&message=Git&color=ef391a&logo=git)](https://source.bookstackapp.com/)
 [![Repo Stats](https://img.shields.io/static/v1?label=GitHub+project&message=stats&color=f27e3f)](https://gh-stats.bookstackapp.com/)