n,o not in the config.
u need to edit the js file (MMM-GoogleMapsTraffic.js)

if u want just replace ur js with the code i use

/* global Module */

/* Magic Mirror
 * Module: MMM-GoogleMapsTraffic
 *
 * By Victor Mora
 * MIT Licensed.
 */

Module.register("MMM-GoogleMapsTraffic", {
	// Module config defaults
	defaults : {
		lat: '',
		lng: '',
		height: '300px',
		width: '300px',
		zoom: 10,
                mapTypeId: 'roadmap',
		disableDefaultUI: true
	},

	getDom: function() {
        var lat = this.config.lat;
        var lng = this.config.lng;

	var wrapper = document.createElement("div");
        wrapper.setAttribute("id", "map");

        wrapper.style.height = this.config.height;
        wrapper.style.width = this.config.width;

        var script = document.createElement("script");
        script.type = "text/javascript";
        script.src = "https://maps.googleapis.com/maps/api/js?key=" + this.config.key;
        document.body.appendChild(script);

	var self = this;
        script.onload = function () {
            var map = new google.maps.Map(document.getElementById("map"), {
            	zoom: self.config.zoom,
                mapTypeId: self.config.mapTypeId,
            	center: {
            		lat: self.config.lat,
            		lng: self.config.lng
            	},
			//disableDefaultUI: self.config.disableDefaultUI
			disableDefaultUI: true,
			styles: [
			{elementType: 'geometry', stylers: [{color: '#242f3e'}]},
			{elementType: 'labels.text.stroke', stylers: [{color: '#242f3e'}]},
			{elementType: 'labels.text.fill', stylers: [{color: '#746855'}]},
			{
			    featureType: 'administrative.locality',
			    elementType: 'labels.text.fill',
			    stylers: [{color: '#d59563'}]
			},
			{
				featureType: 'poi',
				elementType: 'labels.text.fill',
				stylers: [{color: '#d59563'}]
			},
			{
				featureType: 'poi.park',
			        elementType: 'geometry',
			        stylers: [{color: '#263c3f'}]
			},
			{
				featureType: 'poi.park',
				elementType: 'labels.text.fill',
				stylers: [{color: '#6b9a76'}]
			},
			{
				featureType: 'road',
				elementType: 'geometry',
				stylers: [{color: '#38414e'}]
			},
			{
				featureType: 'road',
				elementType: 'geometry.stroke',
					  stylers: [{color: '#212a37'}]
			},
			{
				featureType: 'road',
				elementType: 'labels.text.fill',
					  stylers: [{color: '#9ca5b3'}]
			},
			{
				featureType: 'road.highway',
				elementType: 'geometry',
				stylers: [{color: '#746855'}]
			},
			{
				featureType: 'road.highway',
				elementType: 'geometry.stroke',
				stylers: [{color: '#1f2835'}]
			},
			{
				featureType: 'road.highway',
				elementType: 'labels.text.fill',
				stylers: [{color: '#f3d19c'}]
			},
			{
				featureType: 'transit',
				elementType: 'geometry',
				stylers: [{color: '#2f3948'}]
			},
			{
			        featureType: 'transit.station',
				elementType: 'labels.text.fill',
				stylers: [{color: '#d59563'}]
			},
			{
			        featureType: 'water',
			        elementType: 'geometry',
				stylers: [{color: '#17263c'}]
			},
			{
				featureType: 'water',
				elementType: 'labels.text.fill',
				stylers: [{color: '#515c6d'}]
			},
			{
				featureType: 'water',
				elementType: 'labels.text.stroke',
				stylers: [{color: '#17263c'}]
			}
		]
            });

            var trafficLayer = new google.maps.TrafficLayer();
            trafficLayer.setMap(map);
        };

		return wrapper;
	}

});