Update CI badge/link in README

Author: oschulz

README.md

@@ -3,7 +3,7 @@
 [![Documentation for stable version](https://img.shields.io/badge/docs-stable-blue.svg)](https://oschulz.github.io/BitOperations.jl/stable)
 [![Documentation for development version](https://img.shields.io/badge/docs-dev-blue.svg)](https://oschulz.github.io/BitOperations.jl/dev)
 [![License](http://img.shields.io/badge/license-MIT-brightgreen.svg?style=flat)](LICENSE.md)
-[![Travis Build Status](https://travis-ci.com/oschulz/BitOperations.jl.svg?branch=master)](https://travis-ci.com/oschulz/BitOperations.jl)
+[![Build Status](https://github.com/oschulz/BitOperations.jl/workflows/CI/badge.svg?branch=master)](https://github.com/oschulz/BitOperations.jl/actions?query=workflow%3ACI)
 [![Codecov](https://codecov.io/gh/oschulz/BitOperations.jl/branch/master/graph/badge.svg)](https://codecov.io/gh/oschulz/BitOperations.jl)