Update README.md

Author: satazor

README.md

@@ -1,6 +1,6 @@
 # node-promise-retry
 
-[![NPM version][npm-image]][npm-url] [![Downloads][downloads-image]][npm-url] [![Build Status][travis-image]][travis-url] [![Dependency status][david-dm-image]][david-dm-url] [![Dev Dependency status][david-dm-dev-image]][david-dm-dev-url]
+[![NPM version][npm-image]][npm-url] [![Downloads][downloads-image]][npm-url] [![Build Status][travis-image]][travis-url] [![Dependency status][david-dm-image]][david-dm-url] [![Dev Dependency status][david-dm-dev-image]][david-dm-dev-url] [![Greenkeeper badge][greenkeeper-image]][greenkeeper-url]
 
 [npm-url]:https://npmjs.org/package/promise-retry
 [downloads-image]:http://img.shields.io/npm/dm/promise-retry.svg
@@ -11,6 +11,8 @@
 [david-dm-image]:https://img.shields.io/david/IndigoUnited/node-promise-retry.svg
 [david-dm-dev-url]:https://david-dm.org/IndigoUnited/node-promise-retry?type=dev
 [david-dm-dev-image]:https://img.shields.io/david/dev/IndigoUnited/node-promise-retry.svg
+[greenkeeper-image]:https://badges.greenkeeper.io/IndigoUnited/node-promise-retry.svg
+[greenkeeper-url]:https://greenkeeper.io/
 
 Retries a function that returns a promise, leveraging the power of the [retry](https://github.com/tim-kos/node-retry) module to the promises world.