docs: remove greenkeeper badge

Author: nodkz

README.md

@@ -5,7 +5,6 @@
 [![Downloads stat](https://img.shields.io/npm/dt/mongodb-memory-server.svg)](http://www.npmtrends.com/mongodb-memory-server)
 [![Travis](https://img.shields.io/travis/nodkz/mongodb-memory-server.svg?maxAge=2592000)](https://travis-ci.org/nodkz/mongodb-memory-server)
 [![Commitizen friendly](https://img.shields.io/badge/commitizen-friendly-brightgreen.svg)](http://commitizen.github.io/cz-cli/)
-[![Greenkeeper badge](https://badges.greenkeeper.io/nodkz/mongodb-memory-server.svg)](https://greenkeeper.io/)
 
 This package spins up a actual/real MongoDB Server programmatically from node for testing or mocking during development. By default it holds the data in memory. Fresh spinned up `mongod` process takes about 7Mb of memory. The server will allow you to connect your favorite ODM or client library to the MongoDB Server and run integration tests isolated from each other.