Chore: use flat-square style github actions badge

README.md

@@ -1,5 +1,5 @@
 [![NPM version][npm-image]][npm-url]
-[![Build Status](https://github.com/eslint/eslint/workflows/CI/badge.svg)](https://github.com/eslint/eslint/actions)
+[![Build Status][github-actions-image]](github-actions-url)
 [![Downloads][downloads-image]][downloads-url]
 [![Bountysource](https://www.bountysource.com/badge/tracker?tracker_id=282608)](https://www.bountysource.com/trackers/282608-eslint?utm_source=282608&utm_medium=shield&utm_campaign=TRACKER_BADGE)
 [![Join the chat at https://gitter.im/eslint/eslint](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/eslint/eslint?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
@@ -276,3 +276,5 @@ The following companies, organizations, and individuals support ESLint's ongoing
 [npm-url]: https://www.npmjs.com/package/eslint
 [downloads-image]: https://img.shields.io/npm/dm/eslint.svg?style=flat-square
 [downloads-url]: https://www.npmjs.com/package/eslint
+[github-actions-image]: https://img.shields.io/github/workflow/status/eslint/eslint/CI?style=flat-square
+[github-actions-image]: https://github.com/eslint/eslint/actions