Update CI badge in README.md (#194)

* Update CI badge in README.md

* Update Gem Version badge

README.md

@@ -6,9 +6,8 @@ external programs running in the background on any Ruby / OS combination.
 The code originated in the [selenium-webdriver](https://rubygems.org/gems/selenium-webdriver) gem, but should prove useful as
 a standalone library.
 
-[![Build Status](https://secure.travis-ci.org/enkessler/childprocess.svg)](http://travis-ci.org/enkessler/childprocess)
-[![Build status](https://ci.appveyor.com/api/projects/status/fn2snbcd7kku5myk/branch/dev?svg=true)](https://ci.appveyor.com/project/enkessler/childprocess/branch/dev)
-[![Gem Version](https://badge.fury.io/rb/childprocess.svg)](http://badge.fury.io/rb/childprocess)
+[![CI](https://github.com/enkessler/childprocess/actions/workflows/ci.yml/badge.svg)](https://github.com/enkessler/childprocess/actions/workflows/ci.yml)
+![Gem Version](https://img.shields.io/gem/v/childprocess)
 [![Code Climate](https://codeclimate.com/github/enkessler/childprocess.svg)](https://codeclimate.com/github/enkessler/childprocess)
 [![Coverage Status](https://coveralls.io/repos/enkessler/childprocess/badge.svg?branch=master)](https://coveralls.io/r/enkessler/childprocess?branch=master)