up readme with actions

Author: matbesancon

README.md

@@ -1,7 +1,6 @@
 # StaticGraphs
 
-[![Build Status](https://travis-ci.org/JuliaGraphs/StaticGraphs.jl.svg?branch=master)](https://travis-ci.org/JuliaGraphs/StaticGraphs.jl)
-
+[![Build Status](https://github.com/JuliaGraphs/StaticGraphs.jl/workflows/CI/badge.svg)](https://github.com/JuliaGraphs/StaticGraphs.jl/actions?query=workflow%3ACI+branch%3Amaster)
 [![codecov.io](http://codecov.io/github/JuliaGraphs/StaticGraphs.jl/coverage.svg?branch=master)](http://codecov.io/github/JuliaGraphs/StaticGraphs.jl?branch=master)
 
 Memory-efficient, performant graph structures optimized for large networks.