Fix broken badge in README.md (#145)

Author: lostella

README.md

@@ -1,6 +1,6 @@
 # ProximalOperators.jl
 
-[![Build status](https://github.com/JuliaFirstOrder/ProximalOperators.jl/workflows/CI/badge.svg?branch=master)](https://github.com/JuliaFirstOrder/ProximalOperators.jl/actions?query=workflow%3ACI+branch%3Amaster)
+[![Build status](https://github.com/JuliaFirstOrder/ProximalOperators.jl/workflows/CI/badge.svg?branch=master)](https://github.com/JuliaFirstOrder/ProximalOperators.jl/actions?query=workflow%3ATest+branch%3Amaster)
 [![codecov](https://codecov.io/gh/JuliaFirstOrder/ProximalOperators.jl/branch/master/graph/badge.svg)](https://codecov.io/gh/JuliaFirstOrder/ProximalOperators.jl)
 [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.4020558.svg)](https://doi.org/10.5281/zenodo.4020558)
 [![Aqua QA](https://raw.githubusercontent.com/JuliaTesting/Aqua.jl/master/badge.svg)](https://github.com/JuliaTesting/Aqua.jl)