function parseInteger (parser) {
  if (parser.optionStringNumbers === true) {
    return parseStringNumbers(parser)
  }
  return parseSimpleNumbers(parser)
}
Parse a ':' redis integer response

If stringNumbers is activated the parser always returns numbers as string
This is important for big numbers (number > Math.pow(2, 53)) as js numbers
are 64bit floating point numbers with reduced precision

@param {JavascriptRedisParser} parser
@returns {undefined|number|string}