add d3.js as offline library

genome-vuer/src/index.html

@@ -7,7 +7,7 @@
   <title></title>
   <meta name="description" content="">
   <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
-  <script src="https://d3js.org/d3.v4.min.js"></script>
+  <script src="../lib/d3.js"></script>
   <script src="../lib/vue.js"></script>
   <script src="./js/viz-linear-sequence.js" defer></script>
   <link href="./css/viz-linear-sequence.css" rel="stylesheet">