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<html>
<head>
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/4.13.0/d3.js"></script>
<script src="https://d3js.org/colorbrewer.v1.min.js"></script>
</head>
<body>
<script src="box.js"></script>
</body>
</html>
Modified http://d3js.org/colorbrewer.v1.min.js to a secure url
https://cdnjs.cloudflare.com/ajax/libs/d3/4.13.0/d3.js
https://d3js.org/colorbrewer.v1.min.js