Readme: update Go Report Card to new repo

Signed-off-by: Derek Perkins <derek@derekperkins.com>

README.md

@@ -1,7 +1,7 @@
 [![Maven Central](https://maven-badges.herokuapp.com/maven-central/io.vitess/vitess-jdbc/badge.svg)](https://maven-badges.herokuapp.com/maven-central/io.vitess/vitess-jdbc)
 [![Build Status](https://travis-ci.org/youtube/vitess.svg?branch=master)](https://travis-ci.org/youtube/vitess/builds)
 [![codebeat badge](https://codebeat.co/badges/51c9a056-1103-4522-9a9c-dc623821ea87)](https://codebeat.co/projects/github-com-youtube-vitess)
-[![Go Report Card](https://goreportcard.com/badge/github.com/youtube/vitess)](https://goreportcard.com/report/github.com/youtube/vitess)
+[![Go Report Card](https://goreportcard.com/badge/vitess.io/vitess)](https://goreportcard.com/report/vitess.io/vitess)
 
 # Vitess