docs(readme): add Greenkeeper badge

greenkeeper[bot] · greenkeeper[bot] · commit ef7d535fd6ec · 2018-06-01T22:41:11.000Z
diff --git a/README.md b/README.md
@@ -1,5 +1,7 @@
 # json-editor
 
+[![Greenkeeper badge](https://badges.greenkeeper.io/yourtion/vue-json-ui-editor.svg)](https://greenkeeper.io/)
+
 Edit JSON in UI form with JSON Schema and Vue.js `<json-editor>` component.
 
 ![ScreenShot](screenshot.jpg)
