Display GitHub Action badge instead of an external one

README.md

-# Public APIs [![Build Status](https://api.travis-ci.org/public-apis/public-apis.svg)](https://travis-ci.org/public-apis/public-apis)
+# Public APIs [![Run tests](https://github.com/public-apis/public-apis/workflows/Run%20tests/badge.svg)](https://github.com/public-apis/public-apis/actions?query=workflow%3A%22Run+tests%22)
 
 A collective list of free APIs for use in software and web development.