Fix #2755.

In Node, we now use a CommonJS build with external dependencies, rather than
inlining the dependencies as is done with the UMD bundle. Thus, Node now
automatically defers to the dependent’s main entry; in the case of d3-request,
that means it inherits the XMLHttpRequest polyfill.

A slight wrinkle is that Rollup doesn’t correctly re-export the d3.event symbol
if the dependencies are not inlined. However, this is fixed by patching the
CommonJS build and replacing the event export with a getter.

This commit also removes the rollup-plugin-json dependency, and instead
generates a tiny ES6 module to export the version field from package.json.

index.js

 export {
   version
-} from "./package.json";
+} from "./build/version";
 
 export {
   bisect,

package.json

@@ -18,14 +18,15 @@
     "name": "Mike Bostock",
     "url": "http://bost.ocks.org/mike"
   },
-  "main": "build/d3.js",
+  "main": "build/d3.node.js",
+  "browser": "build/d3.js",
   "jsnext:main": "index",
   "repository": {
     "type": "git",
     "url": "https://github.com/mbostock/d3.git"
   },
   "scripts": {
-    "pretest": "mkdir -p build && rollup -c -o build/d3.js -- index.js",
+    "pretest": "mkdir -p build && node -e 'process.stdout.write(\"export var version = \\\"\" + require(\"./package.json\").version + \"\\\";\\n\");' > build/version.js && rollup -c -o build/d3.js -- index.js && rollup -e `node -e 'process.stdout.write(Object.keys(require(\"./package.json\").dependencies).join(\",\"));'` -f cjs -- index.js | grep -v '^exports.event =' > build/d3.node.js && echo '\nObject.defineProperty(exports, \"event\", {get: function() { return d3Selection.event; }});' >> build/d3.node.js",
     "test": "faucet `find test -name '*-test.js'`",
     "prepublish": "npm run test && uglifyjs build/d3.js -c -m -o build/d3.min.js && rm -f build/d3.zip && zip -j build/d3.zip -- LICENSE README.md build/d3.js build/d3.min.js",
     "postpublish": "VERSION=`node -e 'console.log(require(\"./package.json\").version)'`; git push && cp -v build/d3.js ../d3.github.com/d3.v${VERSION}.js && cp -v build/d3.min.js ../d3.github.com/d3.v${VERSION}.min.js && cd ../d3.github.com && git add d3.v${VERSION}.js d3.v${VERSION}.min.js && git commit -m \"d3 ${VERSION}\" && git push"
@@ -33,7 +34,6 @@
   "devDependencies": {
     "faucet": "0.0",
     "rollup": "0.25",
-    "rollup-plugin-json": "2",
     "rollup-plugin-node-resolve": "1",
     "tape": "4",
     "uglify-js": "2"

rollup.config.js

-import json from "rollup-plugin-json";
 import node from "rollup-plugin-node-resolve";
 
 export default {
-  plugins: [node({jsnext: true}), json()],
+  plugins: [node({jsnext: true})],
   moduleName: "d3",
   format: "umd"
 };