Remove AppVeyor badge

[ci skip]

CONTRIBUTING.md

@@ -1,7 +1,6 @@
 # Contributing [![GitHub contributors](https://img.shields.io/github/contributors/bkimminich/juice-shop.svg)](https://github.com/bkimminich/juice-shop/graphs/contributors) [![JavaScript Style Guide](https://img.shields.io/badge/code%20style-standard-brightgreen.svg)](http://standardjs.com/)
 
 [![Build Status](https://travis-ci.org/bkimminich/juice-shop.svg?branch=master)](https://travis-ci.org/bkimminich/juice-shop)
-[![Build status](https://ci.appveyor.com/api/projects/status/903c6mnns4t7p6fa/branch/master?svg=true)](https://ci.appveyor.com/project/bkimminich/juice-shop/branch/master)
 [![Docker Cloud Build Status](https://img.shields.io/docker/cloud/build/bkimminich/juice-shop.svg)](https://cloud.docker.com/repository/docker/bkimminich/juice-shop/builds)
 [![Test Coverage](https://api.codeclimate.com/v1/badges/2a7af720d39b08a09904/test_coverage)](https://codeclimate.com/github/bkimminich/juice-shop/test_coverage)
 [![Maintainability](https://api.codeclimate.com/v1/badges/2a7af720d39b08a09904/maintainability)](https://codeclimate.com/github/bkimminich/juice-shop/maintainability)