feat(cli): allow assign routes with express.Route() in file JS

[ramonornela]

This PR allow building routes custom using express.router() in source file JS

json-server router.js

Use case ex: router.js

var path = require('path');

module.exports = function() {
	var express = require('express');

	var router = function(router) {
		var expressRouter = express.Router();

		expressRouter.get('/news/me', function(req, res) {
		  var new =  router.db
                           .get('news')
			               .find({ id: 1 })
			               .value();
		  res.json(new);
		});

		return expressRouter;
	}

	return {
		"__source": path.join(__dirname, 'db.json'),
		"__router": router
	}
}