fix appveyor link (#424)

project/google/glog -> project/google-admin/glog

README.md

 [![Build Status](https://img.shields.io/travis/google/glog/master.svg?label=Travis)](https://travis-ci.org/google/glog/builds)
-[![Grunt status](https://img.shields.io/appveyor/ci/google/glog/master.svg?label=Appveyor)](https://ci.appveyor.com/project/google/glog/history)
+[![Grunt status](https://img.shields.io/appveyor/ci/google-admin/glog/master.svg?label=Appveyor)](https://ci.appveyor.com/project/google-admin/glog/history)
 
 This repository contains a C++ implementation of the Google logging
 module.  Documentation for the implementation is in doc/.