Update coverage status badge

Author: lorenzodonini

README.md

@@ -2,7 +2,7 @@
 
 [![Build Status](https://travis-ci.org/lorenzodonini/ocpp-go.svg?branch=master)](https://travis-ci.org/lorenzodonini/ocpp-go)
 [![GoDoc](https://img.shields.io/badge/godoc-reference-5272B4)](https://godoc.org/github.com/lorenzodonini/ocpp-go)
-[![Coverage Status](https://coveralls.io/repos/github/lorenzodonini/ocpp-go/badge.svg?branch=ocpp1.6/examples)](https://coveralls.io/github/lorenzodonini/ocpp-go?branch=ocpp1.6/examples)
+[![Coverage Status](https://coveralls.io/repos/github/lorenzodonini/ocpp-go/badge.svg?branch=master)](https://coveralls.io/github/lorenzodonini/ocpp-go?branch=master)
 [![Go report](https://goreportcard.com/badge/github.com/lorenzodonini/ocpp-go)](https://goreportcard.com/report/github.com/lorenzodonini/ocpp-go)
 
 Open Charge Point Protocol implementation in Go.