docs(readme): replace travis badge with gh action' (#4457)

README.md

@@ -14,7 +14,7 @@
 
 [![NPM version](https://badge.fury.io/js/hexo.svg)](https://www.npmjs.com/package/hexo)
 ![Required Node version](https://img.shields.io/node/v/hexo)
-[![Build Status](https://travis-ci.com/hexojs/hexo.svg?branch=master)](https://travis-ci.com/hexojs/hexo)
+[![Build Status](https://github.com/hexojs/hexo/workflows/Tester/badge.svg)](https://github.com/hexojs/hexo/actions?query=workflow%3ATester)
 [![dependencies Status](https://david-dm.org/hexojs/hexo/status.svg)](https://david-dm.org/hexojs/hexo)
 [![devDependencies Status](https://david-dm.org/hexojs/hexo/dev-status.svg)](https://david-dm.org/hexojs/hexo?type=dev)
 [![Coverage Status](https://coveralls.io/repos/hexojs/hexo/badge.svg?branch=master)](https://coveralls.io/r/hexojs/hexo?branch=master)