added badges from isitmaintained.com (#2517)

README.md

@@ -28,14 +28,17 @@ The vis.js library was initially developed by [Almende B.V](http://almende.com).
 
 [![Dependency Status](https://david-dm.org/almende/vis/status.svg)](https://david-dm.org/almende/vis)
 [![devDependency Status](https://david-dm.org/almende/vis/dev-status.svg)](https://david-dm.org/almende/vis?type=dev)
-[![last version on CDNJS](https://img.shields.io/cdnjs/v/vis.svg)](https://cdnjs.com/libraries/vis)
 
+[![last version on CDNJS](https://img.shields.io/cdnjs/v/vis.svg)](https://cdnjs.com/libraries/vis)
 [![GitHub contributors](https://img.shields.io/github/contributors/almende/vis.svg)](https://github.com/almende/vis/graphs/contributors)
 [![GitHub stars](https://img.shields.io/github/stars/almende/vis.svg)](https://github.com/almende/vis/stargazers)
+
 [![GitHub issues](https://img.shields.io/github/issues/almende/vis.svg)](https://github.com/almende/vis/issues)
+[![Percentage of issues still open](http://isitmaintained.com/badge/open/almende/vis.svg)](http://isitmaintained.com/project/almende/vis "Percentage of issues still open")
+[![Average time to resolve an issue](http://isitmaintained.com/badge/resolution/almende/vis.svg)](http://isitmaintained.com/project/almende/vis "Average time to resolve an issue")
 [![Pending Pull-Requests](http://githubbadges.herokuapp.com/almende/vis/pulls.svg)](https://github.com/almende/vis/pulls)
 
-[![Code Climate](https://codeclimate.com/github/almende/vis/badges/gpa.svg)](https://codeclimate.com/github/almende/vis)
+[![Code Climate](https://codeclimate.com/github/almende/vis/badges/gpa.svg)](https://codeclimate.com/github/almende/vis) 
 
 ## Install