Fix npm package badge in README

Author: Skumring

README.md

@@ -1,5 +1,5 @@
 [![Gem Version](https://badge.fury.io/rb/active_admin_datetimepicker.svg)](http://badge.fury.io/rb/active_admin_datetimepicker)
-[![NPM Version](https://badge.fury.io/js/active_admin_datetimepicker.svg)](https://badge.fury.io/js/active_admin_datetimepicker)
+[![NPM Version](https://badge.fury.io/js/@activeadmin-plugins%2Factive_admin_datetimepicker.svg)](https://badge.fury.io/js/@activeadmin-plugins%2Factive_admin_datetimepicker)
 [![npm](https://img.shields.io/npm/dm/active_admin_datetimepicker.svg)](https://www.npmjs.com/package/@activeadmin-plugins/active_admin_datetimepicker)
 [![Build Status](https://img.shields.io/travis/activeadmin-plugins/active_admin_datetimepicker.svg)](https://travis-ci.org/activeadmin-plugins/active_admin_datetimepicker)
 [![Coverage](https://coveralls.io/repos/activeadmin-plugins/active_admin_datetimepicker/badge.svg?branch=master)](https://coveralls.io/r/activeadmin-plugins/active_admin_datetimepicker)