Restore the timing to store the d3 reference (#2066)

* fix: restore the timing to store the d3 reference, fix #2060

* chore: modify .jshintrc

.jshintrc

@@ -19,6 +19,7 @@
     "jasmine": true,
 
     "globals": {
-        "d3": false
+        "d3": false,
+        "require": false
     }
 }

src/core.js

@@ -1,4 +1,3 @@
-import * as d3 from 'd3';
 import Axis from './axis';
 import CLASS from './class';
 import { isValue, isFunction, isString, isUndefined, isDefined, ceil10, asHalfPixel, diffDomain, isEmpty, notEmpty, getOption, hasValue, sanitise, getPathBox } from './util';
@@ -49,7 +48,7 @@ function Chart(config) {
 
 function ChartInternal(api) {
     var $$ = this;
-    $$.d3 = d3;
+    $$.d3 = window.d3 ? window.d3 : typeof require !== 'undefined' ? require("d3") : undefined;
     $$.api = api;
     $$.config = $$.getDefaultConfig();
     $$.data = {};