readme: update build badge to Test workflow badge

Closes #429

README.md

@@ -1,6 +1,6 @@
 # tmi.js
 
-[![Build Status](https://secure.travis-ci.org/tmijs/tmi.js.png?branch=master)](https://travis-ci.org/tmijs/tmi.js)
+![Test Workflow Status](https://github.com/tmijs/tmi.js/workflows/Test/badge.svg)
 [![Npm Version](https://img.shields.io/npm/v/tmi.js.svg?style=flat)](https://www.npmjs.org/package/tmi.js)
 [![Downloads](https://img.shields.io/npm/dm/tmi.js.svg?style=flat)](https://www.npmjs.org/package/tmi.js)
 [![Issues](https://img.shields.io/github/issues/tmijs/tmi.js.svg?style=flat)](https://github.com/tmijs/tmi.js/issues)