Fix #3055.

rollup.node.js

@@ -6,12 +6,7 @@ rollup.rollup({
   entry: "index.js",
   external: Object.keys(dependencies)
 }).then(function(bundle) {
-  var code = bundle.generate({
-    format: "cjs"
-  }).code.replace(
-    /^exports\.event = (.*);$/m,
-    "Object.defineProperty(exports, \"event\", {get: function() { return $1; }});"
-  );
+  var code = bundle.generate({format: "cjs"}).code + "Object.defineProperty(exports, \"event\", {get: function() { return d3Selection.event; }});\n";
   return new Promise(function(resolve, reject) {
     fs.writeFile("build/d3.node.js", code, "utf8", function(error) {
       if (error) return reject(error);