Use pinned deps in appveyor builds

Author: pimterry

appveyor.yml

@@ -30,8 +30,7 @@ install:
 - cmd: appveyor-tools\secure-file -decrypt certificates/encrypted-win-cert.pfx.enc -secret %CERTIFICATE_FILE_KEY%
 - ps: Install-Product node $env:nodejs_version $env:platform
 - set PATH=%APPDATA%\npm;%PATH%
-- npm install
-- npm update
+- npm ci
 
 build_script:
 - node --version