function readDate(der) {
	if (der.peek() === asn1.Ber.UTCTime) {
		return (utcTimeToDate(der.readString(asn1.Ber.UTCTime)));
	} else if (der.peek() === asn1.Ber.GeneralizedTime) {
		return (gTimeToDate(der.readString(asn1.Ber.GeneralizedTime)));
	} else {
		throw (new Error('Unsupported date format'));
	}
}
Creates validator instance.
Usage: `Ajv(opts)`
@param {Object} opts optional options
@return {Object} ajv instance