chore: avoid win32 related npm@5 bugs

Author: marionebl

appveyor.yml

@@ -4,7 +4,7 @@ environment:
 install:
   - ps: Install-Product node $env:nodejs_version
   - set CI=true
-  - npm -g install npm@latest
+  - npm install -g npm@4
   - set PATH=%APPDATA%\npm;%PATH%
   - npm install
 matrix: