Update README.md

Author: Dean Karn

README.md

@@ -1,7 +1,7 @@
 Library webhooks
 ================
 <img align="right" src="https://raw.githubusercontent.com/go-playground/webhooks/v3/logo.png">![Project status](https://img.shields.io/badge/version-4.0.0-green.svg)
-[![Build Status](https://travis-ci.org/go-playground/webhooks.svg?branch=v3)](https://travis-ci.org/go-playground/webhooks)
+[![Build Status](https://travis-ci.org/go-playground/webhooks.svg?branch=v4)](https://travis-ci.org/go-playground/webhooks)
 [![Coverage Status](https://coveralls.io/repos/go-playground/webhooks/badge.svg?branch=v4&service=github)](https://coveralls.io/github/go-playground/webhooks?branch=v3)
 [![Go Report Card](https://goreportcard.com/badge/go-playground/webhooks)](https://goreportcard.com/report/go-playground/webhooks)
 [![GoDoc](https://godoc.org/gopkg.in/go-playground/webhooks.v4?status.svg)](https://godoc.org/gopkg.in/go-playground/webhooks.v4)