docs(readme): add Greenkeeper badge

greenkeeper[bot] · greenkeeper[bot] · commit 3348900c7616 · 2018-04-10T14:50:45.000Z
diff --git a/README.md b/README.md
@@ -1,5 +1,7 @@
 ## angularjs-input-birthday
 
+[![Greenkeeper badge](https://badges.greenkeeper.io/heyprof/angularjs-input-birthday.svg)](https://greenkeeper.io/)
+
 An AngularJS component to select a birthday date. The package require moment and angular-translate
 
 ### Install
