[nodejs-server] cannot set serverPort

Description

I would like to set serverPort with --additional-properties.
but this arguement is ignored to specify nodejs server mode.

Swagger-codegen version

3.0.26

Swagger declaration file content or url

Command line used for generation

node.js

$ swagger-codegen generate --additional-properties serverPort=8081 -i ./sample.yml -l nodejs-server -o ./tmp
$ cat tmp/index.js
'use strict';

var path = require('path');
var http = require('http');

var oas3Tools = require('oas3-tools');
var serverPort = 8080;

...

[FYI] python-flask

$ swagger-codegen generate --additional-properties serverPort=8081 -i ./sample.yml -l python-flask -o ./tmp

$ cat tmp/Dockerfile
FROM python:3.6-alpine

RUN mkdir -p /usr/src/app
WORKDIR /usr/src/app

COPY requirements.txt /usr/src/app/

RUN pip3 install --no-cache-dir -r requirements.txt

COPY . /usr/src/app

EXPOSE 8081
...

Steps to reproduce

$ swagger-codegen generate --additional-properties serverPort=8081 -i ./sample.yml -l nodejs-server -o ./tmp

Related issues/PRs

Suggest a fix/enhancement

Reproduce the nodejs-server generation command with serverPort=8081 and inspect the generated tmp/index.js, which currently shows 8080. Compare this with the python-flask example and trace how --additional-properties is handled for the nodejs-server generator. Done means the generated server uses the requested port, with a regression test if the generator's test location is identified.