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

This reverts commit 0d581c49.