Make Error tips more clear when it failed testing

[lijiarui]

Chang jekyll/contributors/AUTHOR.md to jekyll/_contributors/AUTHOR.md in error tips.

See: https://github.com/wechaty/wechaty.js.org/pull/1304#issuecomment-924102714

[huan]

In the related issue you provided, the error message is:

    # Subtest: developer profile file (jekyll/_contributors/__AUTHOR__.md) filename must match /[a-z0-9_-.]+/
        not ok 1 - "jekyll/_contributors/Gan-lang.md" should match /\/[a-z0-9_.-]+.md$/

I believe it's clear enough.

Please feel free to let me know if you have any suggestions to improve those messages.