Audit check digit clue for itself

[maiconcarraro]

You can use the existing ISBN from the demo that is 9781781682135, if you replace the last digit with a different number like 4, 9781781682134 it will get invalid and no clues. It would be nice to give a clue/hint similar to the invalid prefix.

Very similar to this:

isbn3/lib/audit.js

Lines 38 to 46 in 08d42be

	const considerAltPrefix = (normalizedIsbn, altPrefix, clues) => {
	const candidateBase = `${altPrefix}${normalizedIsbn.substring(3, 12)}`
	const checkDigit = calculateCheckDigit(candidateBase)
	const candidateData = parse(`${candidateBase}${checkDigit}`)
	if (candidateData != null) {
	const { isbn13h, isbn13, groupname } = candidateData
	clues.push({ message: 'possible prefix error', candidate: isbn13h, isbn13, groupname })
	}
	}