[helix5] add newline at end of default robots.txt and sitemap.xml

[royfielding]

Description
The generated default robots.txt and generated sitemap.xml files do not have a newline at the EOF, which can cause problems with poorly written text-based parsers.

To Reproduce

curl https://www.gjfielding.com/robots.txt
curl https://www.gjfielding.com/sitemap.xml

Expected behavior
Generate a \n at end of last line.

Additional context
The code in src/robots-pipe.js:

  const txt = [
    'User-Agent: *',
    'Allow: /',
    '',
    `Sitemap: https://${prodHost}/sitemap.xml`,
  ].join('\n');

should either have '' at end of list or be a literal like

  const txt = `User-Agent: *
Allow: /

Sitemap: https://${prodHost}/sitemap.xml
`;
 

maybe (I don't have much javascript language experience).

The same join technique is used in sitemap-pipe.js and can be fixed in same way.

[tripodsan]

thanks @royfielding .
I think adding the '' empty line at the end of the array is the easiest to adjust.
pull request welcome :-)