Options typescript interface issue - secret should be optional

[JoHuang]

currently

export interface ConfigOptions {
    secret: string;
    verbose?: boolean | undefined;
    environment?: string[] | undefined;
    ignoreExpiredError?: boolean | undefined;
    ignoreExpired?: boolean | undefined;
    extended?: boolean | undefined;
    excludeOldTransactions?: boolean | undefined;
}

should be

export interface ConfigOptions {
    secret?: string;
    verbose?: boolean | undefined;
    environment?: string[] | undefined;
    ignoreExpiredError?: boolean | undefined;
    ignoreExpired?: boolean | undefined;
    extended?: boolean | undefined;
    excludeOldTransactions?: boolean | undefined;
}

Have to use any to workaround if you don't check auto-renewable purchases.