Remove waffle.io link

Will be shutdown May 16th

README.md

@@ -7,7 +7,6 @@
 <p align="center">
   <a href="https://pion.ly"><img src="https://img.shields.io/badge/pion-logging-gray.svg?longCache=true&colorB=brightgreen" alt="Pion transport"></a>
   <a href="http://gophers.slack.com/messages/pion"><img src="https://img.shields.io/badge/join-us%20on%20slack-gray.svg?longCache=true&logo=slack&colorB=brightgreen" alt="Slack Widget"></a>
-  <a href="https://waffle.io/pion/webrtc"><img src="https://img.shields.io/badge/pm-waffle-gray.svg?longCache=true&colorB=brightgreen" alt="Waffle board"></a>
   <br>
   <a href="https://travis-ci.org/pion/logging"><img src="https://travis-ci.org/pion/logging.svg?branch=master" alt="Build Status"></a>
   <a href="https://godoc.org/github.com/pion/logging"><img src="https://godoc.org/github.com/pion/logging?status.svg" alt="GoDoc"></a>