docs(readme): add Greenkeeper badge

Author: greenkeeper[bot]

README.md

@@ -1,5 +1,7 @@
 # angularjs-typescript-webpack starter
 
+[![Greenkeeper badge](https://badges.greenkeeper.io/vsternbach/angularjs-typescript-webpack.svg)](https://greenkeeper.io/)
+
 This project is an application skeleton for [AngularJS](http://angularjs.org/) 1.7, typescript 2.9 and webpack 4.5
 
 Project uses [angular-ts-decorators](https://github.com/vsternbach/angular-ts-decorators) to mimic angular 2+ style development in angularjs environment with typescript and webpack.