fix: build status badge (#538)

Author: Laerte

Diff for: README.md

@@ -1,6 +1,6 @@
 # MessagePack for Python
 
-[![Build Status](https://travis-ci.org/msgpack/msgpack-python.svg?branch=master)](https://travis-ci.org/msgpack/msgpack-python)
+[![Build Status](https://github.com/msgpack/msgpack-python/actions/workflows/wheel.yml/badge.svg)](https://github.com/msgpack/msgpack-python/actions/workflows/wheel.yml)
 [![Documentation Status](https://readthedocs.org/projects/msgpack-python/badge/?version=latest)](https://msgpack-python.readthedocs.io/en/latest/?badge=latest)
 
 ## What's this