Update README.md

Author: satoryu

README.md

@@ -1,7 +1,7 @@
 # docx
 
 [![Gem Version](https://badge.fury.io/rb/docx.svg)](https://badge.fury.io/rb/docx)
-[![Build Status](https://travis-ci.org/ruby-docx/docx.svg?branch=master)](https://travis-ci.org/ruby-docx/docx)
+[![Ruby](https://github.com/ruby-docx/docx/workflows/Ruby/badge.svg)](https://github.com/ruby-docx/docx/actions?query=workflow%3ARuby)
 [![Coverage Status](https://coveralls.io/repos/github/ruby-docx/docx/badge.svg?branch=master)](https://coveralls.io/github/ruby-docx/docx?branch=master)
 [![Gitter](https://badges.gitter.im/ruby-docx/community.svg)](https://gitter.im/ruby-docx/community?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)