docs(readme): add Greenkeeper badge

greenkeeper[bot] · greenkeeper[bot] · commit 1913fdfe2654 · 2019-05-31T11:25:29.000Z
diff --git a/README.md b/README.md
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 # functional-examples
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+[![Greenkeeper badge](https://badges.greenkeeper.io/dmitriz/functional-examples.svg)](https://greenkeeper.io/)
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 Examples with Functional JavaScript
 
 Heavily annotated examples from the awesome videos
