message: fix(wxa): set zlevel for main layer, fix bug for backgroundColor on wxa ecomfe/echarts-for-weixin#6
diff: @@ -201,6 +201,7 @@ var Painter = function (root, storage, opts) {
  // FIXME Use canvas width and height
  // mainLayer.resize(width, height);
  layers[CANVAS_ZLEVEL] = mainLayer;
  + mainLayer.zlevel = CANVAS_ZLEVEL;
  // Not use common zlevel.
  zlevelList.push(CANVAS_ZLEVEL);
  