Restore production on UMD builds

Author: bcomnes

package.json

@@ -12,7 +12,7 @@
     "prepublish": "run-s build",
     "build": "run-p build:*",
     "build:bundle": "cross-env NODE_ENV=production webpack --config webpack.config.babel.js",
-    "build:umd": "webpack --config webpack.umd.config.babel.js",
+    "build:umd": "cross-env NODE_ENV=production webpack --config webpack.umd.config.babel.js",
     "prebuild": "rimraf build && mkdirp build",
     "test": "eslint src",
     "release": "node ./script/release.js",