remove archaic badges from readme

Author: Qix-

README.md

@@ -1,5 +1,5 @@
 # debug
-[![Build Status](https://travis-ci.org/debug-js/debug.svg?branch=master)](https://travis-ci.org/debug-js/debug)  [![Coverage Status](https://coveralls.io/repos/github/debug-js/debug/badge.svg?branch=master)](https://coveralls.io/github/debug-js/debug?branch=master)  [![Slack](https://visionmedia-community-slackin.now.sh/badge.svg)](https://visionmedia-community-slackin.now.sh/) [![OpenCollective](https://opencollective.com/debug/backers/badge.svg)](#backers)
+[![OpenCollective](https://opencollective.com/debug/backers/badge.svg)](#backers)
 [![OpenCollective](https://opencollective.com/debug/sponsors/badge.svg)](#sponsors)
 
 <img width="647" src="https://user-images.githubusercontent.com/71256/29091486-fa38524c-7c37-11e7-895f-e7ec8e1039b6.png">