use Nokogiri's `parse_noscript_content_as_text` option by default if it's available

See https://github.com/sparklemotion/nokogiri/pull/3231 and https://github.com/sparklemotion/nokogiri/issues/3178 for context.

This is yet another step towards making the server and browser parse identically.

The Nokogiri 1.17 milestone can be followed at https://github.com/sparklemotion/nokogiri/milestone/31 or the tracking issue at https://github.com/sparklemotion/nokogiri/issues/3140