[fix]矢量瓦片大小问题 review by songym

Author: YOUYOUNG

examples/openlayers/mvtvectorlayer_mbstyle_beijing.html

@@ -230,6 +230,7 @@
  format: new ol.format.MVT({
  featureClass: ol.Feature
  }),
+ tileGrid:ol.tilegrid.createXYZ({tileSize:512}),
  tileType: 'ViewBounds'
  };
  vectorLayer = new ol.layer.VectorTile({