Update README.md

remove greenkeeper

Author: alxk

README.md

@@ -7,9 +7,6 @@
  <p align="center">
  <img src="https://travis-ci.com/mwrlabs/dref.svg?branch=master">
  <img src="https://codecov.io/gh/mwrlabs/dref/branch/master/graph/badge.svg">
- <a href="https://greenkeeper.io/">
-  <img src="https://badges.greenkeeper.io/serain/netmap.js.svg">
- </a>
  <a href="https://gitter.im/dref/Lobby/">
   <img src="http://badges.gitter.im/serain/dref.svg">
  </a>