Fix CI badge in README.md

Author: jonathanBieler

README.md

@@ -1,5 +1,5 @@
 # GtkSourceWidget
 
-[![Build Status](https://travis-ci.com/JuliaGtk/GtkSourceWidget.jl.svg?branch=master)](https://travis-ci.com/JuliaGtk/GtkSourceWidget.jl) [![](https://img.shields.io/badge/docs-latest-blue.svg)](https://pkg.julialang.org/docs/GtkSourceWidget/)
+[![Build Status](https://github.com/JuliaGtk/GtkSourceWidget.jl/actions/workflows/CI.yml/badge.svg?branch=master)](https://github.com/JuliaGtk/GtkSourceWidget.jl/actions/workflows/CI.yml?query=branch%3Amaster) [![](https://img.shields.io/badge/docs-latest-blue.svg)](https://pkg.julialang.org/docs/GtkSourceWidget/)
 
 GtkSourceWidget.jl is a Julia wrapper for the Gtk library GtkSourceView that allows showing source code documents (see https://wiki.gnome.org/Projects/GtkSourceView).