Fix link to CI badge (#651)

README.md

@@ -3,7 +3,7 @@
 *StatsBase.jl* is a Julia package that provides basic support for statistics. Particularly, it implements a variety of statistics-related functions, such as scalar statistics, high-order moment computation, counting, ranking, covariances, sampling, and empirical density estimation.
 
 - **Build & Testing Status:**
-  [![Build status](https://github.com/JuliaStats/StatsBase.jl/workflows/CI/badge.svg)]((https://github.com/JuliaStats/StatsBase.jl/actions?query=workflow%3ACI+branch%3Amaster))
+  [![Build status](https://github.com/JuliaStats/StatsBase.jl/workflows/CI/badge.svg)](https://github.com/JuliaStats/StatsBase.jl/actions?query=workflow%3ACI+branch%3Amaster)
   [![Coverage Status](https://coveralls.io/repos/JuliaStats/StatsBase.jl/badge.svg?branch=master)](https://coveralls.io/r/JuliaStats/StatsBase.jl?branch=master)
   [![Coverage Status](http://codecov.io/github/JuliaStats/StatsBase.jl/coverage.svg?branch=master)](http://codecov.io/github/JuliaStats/StatsBase.jl?branch=master)