Update README.md

Update code coverage badge. The URL seems to have changed.

README.md

@@ -9,7 +9,7 @@
 |:-----------------:|:----------------------:|:------------:|
 | [![](https://img.shields.io/badge/docs-stable-blue.svg)](https://juliamanifolds.github.io/Manifolds.jl/stable/) | [![Code Style: Blue](https://img.shields.io/badge/code%20style-blue-4495d1.svg)](https://github.com/invenia/BlueStyle) | [![arXiv](https://img.shields.io/badge/arXiv%20CS.MS-2106.08777-blue.svg)](https://arxiv.org/abs/2106.08777) |
 | [![](https://img.shields.io/badge/docs-dev-blue.svg)](https://juliamanifolds.github.io/Manifolds.jl/latest/) | [![CI](https://github.com/JuliaManifolds/Manifolds.jl/actions/workflows/ci.yml/badge.svg)](https://github.com/JuliaManifolds/Manifolds.jl/actions?query=workflow%3ACI+branch%3Amaster) | [![DOI](https://zenodo.org/badge/190447542.svg)](https://zenodo.org/badge/latestdoi/190447542) |
-| | [![codecov.io](http://codecov.io/github/JuliaManifolds/Manifolds.jl/coverage.svg?branch=master)](https://codecov.io/gh/JuliaManifolds/Manifolds.jl/) |
+| | [![codecov](https://codecov.io/gh/JuliaManifolds/Manifolds.jl/graph/badge.svg?token=yQYUnjAZZN)](https://codecov.io/gh/JuliaManifolds/Manifolds.jl) |
 
 Package __Manifolds.jl__ aims to provide both a unified interface to define and
 use manifolds as well as a library of manifolds to use for your projects.