Update Download badge in README.md (#182)

README.md

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 ![tests](https://github.com/NonlinearOscillations/HarmonicBalance.jl/workflows/Run%20tests/badge.svg?branch=master)
 [![docs](https://img.shields.io/badge/docs-online-blue.svg)](https://nonlinearoscillations.github.io/HarmonicBalance.jl/stable/)
-[![Downloads](https://shields.io/endpoint?url=https://pkgs.genieframework.com/api/v1/badge/HarmonicBalance)](https://pkgs.genieframework.com?packages=HarmonicBalance)
+[![Downloads](https://img.shields.io/badge/dynamic/json?url=http%3A%2F%2Fjuliapkgstats.com%2Fapi%2Fv1%2Fmonthly_downloads%2FHarmonicBalance&query=total_requests&suffix=%2Fmonth&label=Downloads)](https://juliapkgstats.com/pkg/HarmonicBalance)
 
 **HarmonicBalance.jl** is a Julia package for solving nonlinear differential equations using the method of harmonic balance.