Google Map label z-Index not working with GeoJSON. AngularJS Google Maps Directive https://github.com/googlemaps/v3-utility-library/issues/386

<!DOCTYPE html>
<html ng-app="myApp">
<head>
<meta name="viewport" content="initial-scale=1.0, user-scalable=no" />
<script src="geojson.js"></script>
<script src="https://maps.google.com/maps/api/js?libraries=placeses,visualization,drawing,geometry,places"></script>
<script src="https://code.angularjs.org/1.3.15/angular.js"></script>
<script src="https://rawgit.com/allenhwkim/angularjs-google-maps/master/build/scripts/ng-map.js"></script>
<script src="https://googlemaps.github.io/js-map-label/src/maplabel-compiled.js"></script>
<script>
var app = angular.module('myApp', ['ngMap']);
app.controller('MyCtrl', function(NgMap) {
  var vm = this;

  NgMap.getMap().then(function(map) {
    vm.map = map;
    vm.map.data.setStyle(function(feature) {
      return({
        fillColor: feature.getProperty('fill') ? feature.getProperty('fill') : 'transparent',
        strokeWeight: 0.5,
        fillOpacity: feature.getProperty('fillOpacity') ? feature.getProperty('fillOpacity') : 0.5,
        zIndex: 1000
      });
    });
    vm.map.data.addGeoJson(geojson);
    vm.map.data.forEach(function (feature) {
      var centroid = feature.getProperty('centroid');
      var myLatlng = new google.maps.LatLng(centroid.coordinates[1], centroid.coordinates[0]);

      var mapLabel = new MapLabel({
          text: feature.getProperty('Shale_play'),
          position: myLatlng,
          map: vm.map,
          fontSize: 16,
          align: 'center',
          minZoom: 5,
          fontColor: '#0000ff',
          zIndex: 5000
      });

      mapLabel.set('position', myLatlng);
    });
  });
});
</script>
</head>
<body ng-controller="MyCtrl as vm">
  <ng-map zoom="8" center="35.3944545,-92.78723"></ng-map>
</body>
</html>

  var geojson = {
	"type": "FeatureCollection",
	"features": [{
	"type": "Feature",
	"properties": {
		"id": "geology_tightOilGas_eia20160311",
		"fillOpacity": "0.8",
		"fill": "#00aa22",
		"Basin": "Arkoma",
		"Lithology": "Shale",
		"Shale_play": "Fayetteville",
		"Source": "EIA",
		"Area_sq_mi": 5852.69474734,
		"Area_sq_km": 15158.4098071,
		"Age_shale": "Mississippian",
		"centroid": {
			"type": "Point",
			"coordinates": [-92.78723, 35.3944545]
		}
	},
	"geometry": {
		"type": "MultiPolygon",
		"coordinates": [
			[
				[
					[-94.277701, 35.202423],
					[-94.382715, 35.322647],
					[-94.393411, 35.533806],
					[-94.36331599899995, 35.638342],
					[-94.24130399899997, 35.682679],
					[-94.023528, 35.690577],
					[-93.875907, 35.691057],
					[-93.491065, 35.684045],
					[-92.952118, 35.658092],
					[-92.664754, 35.666656],
					[-92.30350699899998, 35.677098],
					[-91.918848, 35.628261],
					[-91.475479, 35.601242],
					[-91.181049, 35.59428500100006],
					[-91.274519, 35.529656],
					[-91.388323, 35.449603],
					[-91.544307, 35.31595599900004],
					[-91.73661700099996, 35.176988],
					[-91.867632, 35.102377],
					[-92.012094, 35.097852],
					[-92.29381300099999, 35.102714],
					[-92.709335, 35.13337],
					[-93.396545, 35.153332],
					[-94.01489300099996, 35.168451],
					[-94.277701, 35.202423]
				]
			]
		]
	}
}]
};