build: fixes golang 1.8 build on windows

appveyor.yml

@@ -10,9 +10,10 @@ environment:
   GOVERSION: 1.8
 
 install:
+  - rmdir c:\go /s /q
   # install nodejs and npm
   - ps: Install-Product node $env:nodejs_version
-  - npm install -g yarn --quiet
+  - npm install -g yarn --silent
   - yarn install --pure-lockfile --no-progress
   - npm install -g grunt-cli
   - appveyor DownloadFile https://storage.googleapis.com/golang/go%GOVERSION%.windows-amd64.zip