message: chore: Add Github Actions status badge
  Removes Circle CI badge.
diff: # <img src="docs_app/assets/Rx_Logo_S.png" alt="RxJS Logo" width="86" height="86"> RxJS: Reactive Extensions For JavaScript
  -[![CircleCI](https://circleci.com/gh/ReactiveX/rxjs/tree/master.svg?style=svg)](https://circleci.com/gh/ReactiveX/rxjs/tree/master)
  +![CI](https://github.com/reactivex/rxjs/workflows/CI/badge.svg)
  [![npm version](https://badge.fury.io/js/rxjs.svg)](http://badge.fury.io/js/rxjs)
  [![Join the chat at https://gitter.im/Reactive-Extensions/RxJS](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/Reactive-Extensions/RxJS?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
  