Read long-option value from CLI arguments.
@param {string} option
@returns {string}
function readOpt(option) {
    const prefix = `${option}=`;

    for (let i = 0, len = process.argv.length, arg; i < len; i++) {
        arg = process.argv[i];

        if (arg === option) {
            return process.argv[i+1];
        } else if (arg.indexOf(prefix) === 0) {
            return arg.substr(prefix.length);
        }
    }
}