fixes #4655 assets are not invalidated after a plugin change. To fix this issue (at least for now) we always compare the cache buster. For JavaScript in production this is always fast as the hash is based only on plugin names + version. For css we have to concat the content of all raw css/less files which should be still fast, especially since the css is cached in the browser afterwards. @Julien let me know what you think about this and we can change it otherwise