Does not load traffic layer by default

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This can not show traffic by default, I have to press the traffic button twice to cycle it. there does not seem to be a working method to show traffic on load.

My code looks like this:

`
mapboxgl.accessToken = 'redacted_privatekey_';
var map = new mapboxgl.Map({
container: 'map',
style: 'mapbox://styles/mapbox/streets-v11',
zoom: 8,
center: [-122, 47.8],
});
map.on('load', function() {
map.addControl(new mapboxgl.NavigationControl());
map.addControl(new MapboxTraffic({showTraffic: true}));
});
`

Start by locating the MapboxTraffic control and its handling of the showTraffic option, then reproduce the issue with the map initialization snippet in this report. Done means traffic is visible immediately after the map loads with showTraffic enabled, without pressing the traffic button twice.

Written by the indexing model from the issue text.