docs(readme): add Greenkeeper badge

greenkeeper[bot] · greenkeeper[bot] · commit 216ddca25f76 · 2018-09-16T02:59:35.000Z
diff --git a/README.md b/README.md
@@ -1,4 +1,4 @@
-# optional-chain [![travis-ci](https://travis-ci.org/yayoc/optional-chain.svg?branch=master)](https://travis-ci.org/yayoc/optional-chain)
+# optional-chain [![travis-ci](https://travis-ci.org/yayoc/optional-chain.svg?branch=master)](https://travis-ci.org/yayoc/optional-chain) [![Greenkeeper badge](https://badges.greenkeeper.io/yayoc/optional-chain.svg)](https://greenkeeper.io/)
 
 Optional chaining implementation in TypeScript.  
 Uses [`option type`](https://en.wikipedia.org/wiki/Option_type)

Original file line number	Diff line number	Diff line change
`@@ -1,4 +1,4 @@`
`1`		`-# optional-chain [![travis-ci](https://travis-ci.org/yayoc/optional-chain.svg?branch=master)](https://travis-ci.org/yayoc/optional-chain)`
	`1`	`+# optional-chain [![travis-ci](https://travis-ci.org/yayoc/optional-chain.svg?branch=master)](https://travis-ci.org/yayoc/optional-chain) [![Greenkeeper badge](https://badges.greenkeeper.io/yayoc/optional-chain.svg)](https://greenkeeper.io/)`
`2`	`2`
`3`	`3`	`Optional chaining implementation in TypeScript.`
`4`	`4`	Uses [`option type`](https://en.wikipedia.org/wiki/Option_type)