duration property in JSON example uses incorrect syntax (number instead of ISO 8601 string format)

[danielweck]

https://w3c.github.io/audiobooks/#audio-simple

https://www.w3.org/TR/audiobooks/#audio-simple

Snippet:

 "readingOrder": [
    {
      "url": "http://www.archive.org/download/flatland_rg_librivox/flatland_1_abbott.mp3",
      "encodingFormat": "audio/mpeg",
      "duration": 1371,
      "name": "Part 1, Sections 1 - 3"
    }
]

References:

• https://www.w3.org/TR/pub-manifest/#duration
• https://en.wikipedia.org/wiki/ISO_8601#Durations

[iherman]

Thanks @danielweck, I have marked this as an erratum for the spec.

cc @wareid @mattgarrish