update ci badge

Author: ablaom

README.md

@@ -1,6 +1,6 @@
 # DataScienceTutorials.jl
 
-Latest CI build: [![Tutorials status](https://travis-ci.com/alan-turing-institute/DataScienceTutorials.jl.svg?branch=master)](https://travis-ci.com/alan-turing-institute/DataScienceTutorials.jl) with
+Latest CI build: [![Tutorials status](https://github.com/alan-turing-institute/DataScienceTutorials.jl/workflows/CI/badge.svg)](https://github.com/alan-turing-institute/DataScienceTutorials.jl/actions) with
 
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 [336ed68f] CSV v0.6.2