README.md: update Build Status badge

Author: joelanford

README.md

@@ -1,6 +1,6 @@
 # helm-operator
 
-[![Build Status](https://travis-ci.org/joelanford/helm-operator.svg?branch=master)](https://travis-ci.org/joelanford/helm-operator)
+[![Build Status](https://github.com/joelanford/helm-operator/workflows/CI/badge.svg?branch=master)
 [![Coverage Status](https://coveralls.io/repos/github/joelanford/helm-operator/badge.svg?branch=master)](https://coveralls.io/github/joelanford/helm-operator?branch=master)
 
 Experimental refactoring of the operator-framework's helm operator