Update pkg.go.gev link

Was not updated for /v2 release

README.md

@@ -10,7 +10,7 @@
   <a href="https://pion.ly/slack"><img src="https://img.shields.io/badge/join-us%20on%20slack-gray.svg?longCache=true&logo=slack&colorB=brightgreen" alt="Slack Widget"></a>
   <br>
   <a href="https://travis-ci.org/pion/dtls"><img src="https://travis-ci.org/pion/dtls.svg?branch=master" alt="Build Status"></a>
-  <a href="https://pkg.go.dev/github.com/pion/dtls"><img src="https://godoc.org/github.com/pion/dtls?status.svg" alt="GoDoc"></a>
+  <a href="https://pkg.go.dev/github.com/pion/dtls/v2"><img src="https://godoc.org/github.com/pion/dtls?status.svg" alt="GoDoc"></a>
   <a href="https://codecov.io/gh/pion/dtls"><img src="https://codecov.io/gh/pion/dtls/branch/master/graph/badge.svg" alt="Coverage Status"></a>
   <a href="https://goreportcard.com/report/github.com/pion/dtls"><img src="https://goreportcard.com/badge/github.com/pion/dtls" alt="Go Report Card"></a>
   <a href="https://www.codacy.com/app/Sean-Der/dtls"><img src="https://api.codacy.com/project/badge/Grade/18f4aec384894e6aac0b94effe51961d" alt="Codacy Badge"></a>