docs: lowercase Codecov url

Author: tobiasehlert

README.md

@@ -1,7 +1,7 @@
 # TibiaData API in Golang
 
 [![GitHub CI](https://img.shields.io/github/actions/workflow/status/tibiadata/tibiadata-api-go/build.yml?branch=main&logo=github)](https://github.com/tibiadata/tibiadata-api-go/actions/workflows/build.yml)
-[![Codecov](https://codecov.io/gh/TibiaData/tibiadata-api-go/branch/main/graph/badge.svg?token=PSBNLBI10C)](https://codecov.io/gh/TibiaData/tibiadata-api-go)
+[![Codecov](https://codecov.io/gh/tibiadata/tibiadata-api-go/branch/main/graph/badge.svg?token=PSBNLBI10C)](https://codecov.io/gh/tibiadata/tibiadata-api-go)
 [![GitHub go.mod version](https://img.shields.io/github/go-mod/go-version/tibiadata/tibiadata-api-go?logo=go)](https://github.com/tibiadata/tibiadata-api-go/blob/main/go.mod)
 [![GitHub release](https://img.shields.io/github/v/release/tibiadata/tibiadata-api-go?sort=semver&logo=github)](https://github.com/tibiadata/tibiadata-api-go/releases)
 [![Docker image size (tag)](https://img.shields.io/docker/image-size/tibiadata/tibiadata-api-go/latest?logo=docker)](https://hub.docker.com/r/tibiadata/tibiadata-api-go)