fix branch for coveralls badge

Author: Johann-S

README.md

@@ -62,7 +62,7 @@ Read the [Getting started page](https://getbootstrap.com/docs/4.0/getting-starte
 [![NuGet](https://img.shields.io/nuget/vpre/bootstrap.svg)](https://www.nuget.org/packages/bootstrap/absoluteLatest)
 [![peerDependencies Status](https://img.shields.io/david/peer/twbs/bootstrap.svg)](https://david-dm.org/twbs/bootstrap?type=peer)
 [![devDependency Status](https://img.shields.io/david/dev/twbs/bootstrap.svg)](https://david-dm.org/twbs/bootstrap?type=dev)
-[![Coverage Status](https://coveralls.io/repos/github/twbs/bootstrap/badge.svg?branch=master)](https://coveralls.io/github/twbs/bootstrap?branch=v4-dev)
+[![Coverage Status](https://img.shields.io/coveralls/github/twbs/bootstrap/v4-dev.svg)](https://coveralls.io/github/twbs/bootstrap?branch=v4-dev)
 [![CSS gzip size](http://img.badgesize.io/twbs/bootstrap/v4-dev/dist/css/bootstrap.min.css?compression=gzip&label=CSS+gzip+size)](https://github.com/twbs/bootstrap/tree/v4-dev/dist/css/bootstrap.min.css)
 [![JS gzip size](http://img.badgesize.io/twbs/bootstrap/v4-dev/dist/js/bootstrap.min.js?compression=gzip&label=JS+gzip+size)](https://github.com/twbs/bootstrap/tree/v4-dev/dist/js/bootstrap.min.js)