header will not be detected when some content are placed before h1

Minor improvements to the service workers section of the theme docs

This reverts commit 0bc2b51e.

 Bump downstream dep "register-service-worker" since https://github.com/yyx990803/register-service-worker/pull/9 has been merged.

1. You can write HTML(Vue) anywhere in the header as long as it is not wrapped by code(`).
2. The HTML wrapped by code will be shown as it is.
3. A good practice when using HTML in a header is to leave a space between plain text and HTML.

Add lang facetFilters presets by following VuePress's i18n design logic