Update README.md

Changed build status badge to Github action.

Author: Chessray

README.md

@@ -2,7 +2,7 @@
 Helpful additions to MapStruct when using the Spring Framework.
 
 [![License](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](https://opensource.org/licenses/Apache-2.0)
-[![Build Status](https://img.shields.io/travis/mapstruct/mapstruct-spring-extensions.svg)](https://travis-ci.org/mapstruct/mapstruct-spring-extensions)
+[![Build Status](https://github.com/mapstruct/mapstruct-spring-extensions/workflows/CI/badge.svg?branch=master)](https://github.com/mapstruct/mapstruct-spring-extensions/actions?query=branch%3Amaster+workflow%3ACI)
 [![Coverage Status](https://img.shields.io/codecov/c/github/mapstruct/mapstruct-spring-extensions.svg)](https://codecov.io/gh/mapstruct/mapstruct-spring-extensions)
 [![Code Quality: Java](https://img.shields.io/lgtm/grade/java/g/mapstruct/mapstruct-spring-extensions.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/mapstruct/mapstruct-spring-extensions/context:java)
 [![Total Alerts](https://img.shields.io/lgtm/alerts/g/mapstruct/mapstruct-spring-extensions.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/mapstruct/mapstruct-spring-extensions/alerts)