Removed greenkeeper badge

Author: delvedor

README.md

@@ -1,7 +1,5 @@
 # fast-json-stringify  [![Build Status](https://travis-ci.org/fastify/fast-json-stringify.svg?branch=master)](https://travis-ci.org/fastify/fast-json-stringify)
 
-[![Greenkeeper badge](https://badges.greenkeeper.io/fastify/fast-json-stringify.svg)](https://greenkeeper.io/)
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 __fast-json-stringify__ is x1-4 times faster than `JSON.stringify()`.
 It is particularly suited if you are sending small JSON payloads, the
 advantages reduces on large payloads.