use rollup for umd build

package.json

@@ -4,12 +4,13 @@
   "description": "Extensibly serialize & deserialize Draft.js ContentState",
   "main": "lib/index.js",
   "module": "esm/index.js",
+  "browser": "dist/draft-convert.js",
   "repository": "HubSpot/draft-convert",
   "scripts": {
     "build": "npm run build:cjs && npm run build:esm && npm run build:umd",
     "build:cjs": "cross-env BABEL_ENV=cjs babel src --out-dir lib",
     "build:esm": "cross-env BABEL_ENV=esm babel src --out-dir esm",
-    "build:umd": "wp",
+    "build:umd": "rollup -c",
     "jest": "jest",
     "jest:watch": "jest --watch",
     "jest:debug": "node --debug-brk --inspect ./node_modules/.bin/jest -i",
@@ -66,8 +67,11 @@
     "react": "^15.4.2",
     "react-dom": "^15.4.2",
     "rimraf": "2.5.4",
-    "webpack": "^4.35.3",
-    "webpack-nano": "^0.6.2"
+    "rollup": "1.18.0",
+    "rollup-plugin-commonjs": "^10.0.2",
+    "rollup-plugin-node-resolve": "^5.2.0",
+    "rollup-plugin-replace": "^2.2.0",
+    "rollup-plugin-terser": "^5.1.1"
   },
   "jest": {
     "testRegex": "/test/spec/.*\\.js$"

rollup.config.js

@@ -0,0 +1,32 @@
+import nodeResolve from 'rollup-plugin-node-resolve';
+import commonjs from 'rollup-plugin-commonjs';
+import replace from 'rollup-plugin-replace';
+import { terser } from 'rollup-plugin-terser';
+
+const globals = {
+  'draft-js': 'Draft',
+  immutable: 'Immutable',
+  react: 'React',
+  'react-dom/server': 'ReactDOMServer',
+};
+
+const bundle = (env) => ({
+  input: 'esm/index.js',
+  external: Object.keys(globals),
+  output: {
+    globals,
+    file: env === 'production' ? 'dist/draft-convert.min.js' : 'dist/draft-convert.js' ,
+    format: 'umd',
+    name: 'DraftConvert',
+  },
+  plugins: [
+    nodeResolve(),
+    commonjs(),
+    replace({
+      'process.env.NODE_ENV': JSON.stringify(env)
+    }),
+    env === 'production' && terser(),
+  ].filter(Boolean),
+})
+
+export default [bundle('production'), bundle('development')]