Replace Travis CI status badge with workflow status badge (TooTallNate#80)

Author: lpinca

README.md

@@ -1,7 +1,7 @@
 https-proxy-agent
 ================
 ### An HTTP(s) proxy `http.Agent` implementation for HTTPS
-[![Build Status](https://travis-ci.org/TooTallNate/node-https-proxy-agent.svg?branch=master)](https://travis-ci.org/TooTallNate/node-https-proxy-agent)
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 This module provides an `http.Agent` implementation that connects to a specified
 HTTP or HTTPS proxy server, and can be used with the built-in `https` module.