add jspm package.json config

package.json

@@ -27,6 +27,11 @@
   },
   "main": "index.js",
   "browserify": "index-browserify.js",
+  "jspm": {
+    "main": "d3.js",
+    "files": ["d3.js"],
+    "buildConfig": { "uglify": true }
+  },
   "jam": {
     "main": "d3.js",
     "shim": {