ensure the build folder is cleaned

Jenkinsfile

@@ -8,7 +8,7 @@ pipeline {
  steps {
  sh '''cd src
  npm install
- npx presskit build --output ../out --pretty-links --collapse-menu'''
+ npx presskit build --output ../out --pretty-links --collapse-menu --clean-build-folder'''
  sh '''rm -rf /var/www/press/*
  cp -r out/. /var/www/press'''
  }