README.md: update badge SVG

The badge SVG is updated to the official badge for pkg.go.dev.

Change-Id: Ib9f09e1661ee18f854786098ff3528d4175cf0cb
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/275935
Trust: Julie Qiu <julie@golang.org>
Trust: Joe Tsai <thebrokentoaster@gmail.com>
Run-TryBot: Julie Qiu <julie@golang.org>
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
diff --git a/README.md b/README.md
index 02c5d98..58892f2 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # Go support for Protocol Buffers
 
-[![GoDev](https://img.shields.io/static/v1?label=godev&message=reference&color=00add8)](https://pkg.go.dev/mod/google.golang.org/protobuf)
+[![Go Reference](https://pkg.go.dev/badge/google.golang.org/protobuf.svg)](https://pkg.go.dev/mod/google.golang.org/protobuf)
 [![Build Status](https://travis-ci.org/protocolbuffers/protobuf-go.svg?branch=master)](https://travis-ci.org/protocolbuffers/protobuf-go)
 
 This project hosts the Go implementation for