function parseCommanderInt (value, _unused) {
  const parsedValue = parseInt(value, 10)
  if (isNaN(parsedValue) || parsedValue < 1) {
    throw new InvalidArgumentError('Not a positive integer.')
  }
  return parsedValue
}
Commander parser that converts a string to an integer.

@param {string} value - The value from commander.
@param {*} _unused - Unused.
@returns {number} The value parsed as a number.
@throws {InvalidArgumentError} If the arg is not valid.
@see https://github.com/tj/commander.js/wiki/Class:-Option#argparserfn