Update README.md

Author: ddworak

README.md

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 # AVSystem Commons Library for Scala
 
-[![Build Status](https://travis-ci.org/AVSystem/scala-commons.svg?branch=master)](https://travis-ci.org/AVSystem/scala-commons)
+[![Continuous Integration](https://github.com/AVSystem/scala-commons/actions/workflows/ci.yml/badge.svg)](https://github.com/AVSystem/scala-commons/actions/workflows/ci.yml)
 [![Maven Central](https://maven-badges.herokuapp.com/maven-central/com.avsystem.commons/commons-core_2.12/badge.svg)](https://maven-badges.herokuapp.com/maven-central/com.avsystem.commons/commons-core_2.13)
 
 **[API reference](http://avsystem.github.io/scala-commons/api/com/avsystem/commons/index.html)**