更新chart.js版本，添加chart.js的datalabels插件

ureport2-js/package.json

@@ -19,7 +19,8 @@
     "bootbox": "^4.4.0",
     "bootstrap": "^3.3.7",
     "bootstrap-colorpicker": "^2.5.0",
-    "chart.js": "^2.6.0",
+    "chart.js": "^2.7.2",
+    "chartjs-plugin-datalabels": "^0.3.0",
     "codemirror": "^5.23.0",
     "completer": "^0.1.3",
     "handsontable": "^0.32.0",