docs(readme): add Greenkeeper badge

greenkeeper[bot] · greenkeeper[bot] · commit 6d24f48f3ebd · 2017-09-09T19:40:25.000Z
diff --git a/README.md b/README.md
@@ -1,5 +1,7 @@
 # riemann-query-parser
 
+[![Greenkeeper badge](https://badges.greenkeeper.io/nextorigin/riemann-query-parser.svg)](https://greenkeeper.io/)
+
 [![Build Status][ci-master]][travis-ci]
 [![Coverage Status][coverage-master]][coveralls]
 [![Dependency Status][dependency]][david]
