Update README.md

Author: garyb

README.md

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 # purescript-codec-argonaut
 
 [![Latest release](http://img.shields.io/github/release/garyb/purescript-codec-argonaut.svg)](https://github.com/garyb/purescript-codec-argonaut/releases)
-[![Build Status](https://travis-ci.org/garyb/purescript-codec-argonaut.svg?branch=master)](https://travis-ci.org/garyb/purescript-codec-argonaut)
+![Build Status](https://github.com/garyb/purescript-codec-argonaut/actions/workflows/ci.yml/badge.svg)
 
 Bi-directional codecs for [argonaut](https://github.com/purescript-contrib/purescript-argonaut-core).