Updated package.json to include d3's license

package.json

@@ -37,5 +37,11 @@
   },
   "scripts": {
     "test": "node_modules/.bin/vows; echo"
+  },
+  "licenses": [
+    {
+      "type": "BSD",
+      "url": "https://github.com/mbostock/d3/blob/master/LICENSE"
     }
+  ]
 }