Update README to fix reference URL

R.I.P. godoc.org

Author: shibukawa

README.md

@@ -1,7 +1,7 @@
 go-sqlite3
 ==========
 
-[![GoDoc Reference](https://godoc.org/github.com/mattn/go-sqlite3?status.svg)](http://godoc.org/github.com/mattn/go-sqlite3)
+[![Go Reference](https://pkg.go.dev/badge/github.com/mattn/go-sqlite3.svg)](https://pkg.go.dev/github.com/mattn/go-sqlite3)
 [![GitHub Actions](https://github.com/mattn/go-sqlite3/workflows/Go/badge.svg)](https://github.com/mattn/go-sqlite3/actions?query=workflow%3AGo)
 [![Financial Contributors on Open Collective](https://opencollective.com/mattn-go-sqlite3/all/badge.svg?label=financial+contributors)](https://opencollective.com/mattn-go-sqlite3) 
 [![codecov](https://codecov.io/gh/mattn/go-sqlite3/branch/master/graph/badge.svg)](https://codecov.io/gh/mattn/go-sqlite3)