Add build script

package.json

@@ -3,10 +3,8 @@
   "repository": "unpkg/unpkg.com",
   "scripts": {
     "start": "heroku local -f Procfile.local",
-    "build": "npm run build-assets && npm run build-lib",
-    "build-assets": "NODE_ENV=production webpack -p --json > stats.json",
-    "build-lib": "rimraf lib && babel ./modules -d lib --copy-files",
-    "heroku-postbuild": "npm run build",
+    "build": "node ./tools/build.js",
+    "heroku-postbuild": "node ./tools/build.js",
     "lint": "eslint modules",
     "test": "npm run lint"
   },

tools/build.js

@@ -0,0 +1,16 @@
+const { execSync } = require('child_process')
+
+console.log('Building CommonJS modules ...')
+
+execSync('rimraf lib && babel ./modules -d lib --copy-files', {
+  stdio: 'inherit'
+})
+
+console.log('\nBuilding client bundles ...')
+
+execSync('webpack -p --json > stats.json', {
+  stdio: 'inherit',
+  env: Object.assign({}, process.env, {
+    NODE_ENV: 'production'
+  })
+})