[docs] correct a typo

[iseunghan]

hello, i find a typo in securing-node-red

I think it's a typo below :

https: function() {
    return new Promise((resolve, reject) => {
        var key, cert;
        // Do some work to obtain valid certificates
        // ...
        resolve({
            key: key
            cert: ccert    // * type
        })
    });
}

and then i correct a type:

https: function() {
    return new Promise((resolve, reject) => {
        var key, cert;
        // Do some work to obtain valid certificates
        // ...
        resolve({
            key: key
            cert: cert    // * correct a type
        })
    });
}

[linux-foundation-easycla]

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• ✅ login: iseunghan / name: Seunghan Lee (6434e7e)