Update README.md

Add goreport badge

Author: Dean Karn

README.md

@@ -4,6 +4,7 @@ Package validator
 [![Join the chat at https://gitter.im/bluesuncorp/validator](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/go-playground/validator?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 [![Build Status](https://semaphoreci.com/api/v1/projects/ec20115f-ef1b-4c7d-9393-cc76aba74eb4/523019/badge.svg)](https://semaphoreci.com/joeybloggs/validator)
 [![Coverage Status](https://coveralls.io/repos/go-playground/validator/badge.svg?branch=v8-development&service=github)](https://coveralls.io/github/go-playground/validator?branch=v8-development)
+[![Go Report Card](http://goreportcard.com/badge/go-playground/validator)](http://goreportcard.com/report/go-playground/validator)
 [![GoDoc](https://godoc.org/gopkg.in/go-playground/validator.v8?status.svg)](https://godoc.org/gopkg.in/go-playground/validator.v8)
 
 Package validator implements value validations for structs and individual fields based on tags.