Fix nulldb errors arising in Rails 5.2 (#108)

containers/zammad/setup.sh

@@ -33,8 +33,10 @@ if [ "$1" = 'install' ]; then
   bundle install --without test development mysql
   contrib/packager.io/fetch_locales.rb
   sed -e 's#.*adapter: postgresql#  adapter: nulldb#g' -e 's#.*username:.*#  username: postgres#g' -e 's#.*password:.*#  password: \n  host: zammad-postgresql\n#g' < contrib/packager.io/database.yml.pkgr > config/database.yml
+  sed -i "/require 'rails\/all'/a require\ 'nulldb'" config/application.rb
   sed -i '/# Use a different logger for distributed setups./a \ \ config.logger = Logger.new(STDOUT)' config/environments/production.rb
   sed -i 's/.*scheduler_\(err\|out\).log.*//g' script/scheduler.rb
+  touch db/schema.rb
   bundle exec rake assets:precompile
   rm -r tmp/cache
   chown -R "${ZAMMAD_USER}":"${ZAMMAD_USER}" "${ZAMMAD_TMP_DIR}"