Use rollup for build

package.json

@@ -2,13 +2,12 @@
   "name": "when-dom-ready",
   "version": "1.2.5",
   "description": "$(document).ready() for the 21st century",
-  "main": "dist/index.js",
+  "main": "dist/index.umd.js",
+  "module": "dist/index.es2015.js",
   "scripts": {
     "prebuild": "rm -rf dist",
-    "build": "babel -d dist src",
-    "prebuild:map": "npm run prebuild",
-    "build:map": "babel --source-maps=true -d dist src",
-    "pretest": "npm run build:map",
+    "build": "rollup -c",
+    "pretest": "npm run build",
     "lint": "xo",
     "test": "nyc ava",
     "coverage": "nyc report --reporter=text-lcov | coveralls",
@@ -51,13 +50,14 @@
   "dependencies": {},
   "devDependencies": {
     "ava": "^0.17.0",
-    "babel-cli": "^6.22.2",
     "babel-plugin-array-includes": "^2.0.3",
     "babel-plugin-transform-es2015-arrow-functions": "^6.22.0",
     "browser-env": "^2.0.19",
     "coveralls": "^2.11.15",
     "jsdom": "^9.9.1",
     "nyc": "^10.0.0",
+    "rollup": "^0.41.4",
+    "rollup-plugin-babel": "^2.7.1",
     "xo": "^0.17.1"
   }
 }

rollup.config.js

@@ -0,0 +1,23 @@
+import babel from 'rollup-plugin-babel';
+
+const pkg = require('./package.json');
+
+export default {
+  entry: 'src/index.js',
+  plugins: [
+    babel(),
+  ],
+  targets: [
+    {
+      dest: pkg.main,
+      format: 'umd',
+      moduleName: 'whenDomReady',
+      sourceMap: true
+    },
+    {
+      dest: pkg.module,
+      format: 'es',
+      sourceMap: true
+    }
+  ]
+};