Update README.md

README.md

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 # package extnetip
 [![Go Reference](https://pkg.go.dev/badge/github.com/gaissmai/extnetip.svg)](https://pkg.go.dev/github.com/gaissmai/extnetip#section-documentation)
 [![CI](https://github.com/gaissmai/extnetip/actions/workflows/go.yml/badge.svg)](https://github.com/gaissmai/extnetip/actions/workflows/go.yml)
-[![Coverage Status](https://coveralls.io/repos/github/gaissmai/extnetip/badge.svg)](https://coveralls.io/github/gaissmai/extnetip)
+[![Coverage Status](https://coveralls.io/repos/github/gaissmai/extnetip/badge.svg?branch=master)](https://coveralls.io/github/gaissmai/extnetip?branch=master)
 [![Go Report Card](https://goreportcard.com/badge/github.com/gaissmai/extnetip)](https://goreportcard.com/report/github.com/gaissmai/extnetip)
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)