Make address postcode required

[Aslam97]

Is your feature request related to a problem? Please describe.
I dont get any error when making a payment with auto create order that provided from authorize(). this because i dont provide postcode in the address.

Describe the solution you'd like
Make postcode in address required since ValidateCartForOrder required postcode to be fill.

[glennjacobs]

Not all countries have postcodes. Probably needs more discussion.

[Aslam97]

Not all countries have postcodes. Probably needs more discussion.

if thats the case. i guess by removing postcode from ValidateCartForOrder solved it?

    /**
     * Return the address rules for validation.
     *
     * @return array
     */
    private function getAddressRules()
    {
        return [
            'country_id' => 'required',
            'first_name' => 'required',
            'line_one'   => 'required',
            'city'       => 'required',
            'postcode'   => 'required',
        ];
    }