Fix webpack 4 build (#4064)

* Fix webpack 4 build

Author: snowystinger

examples/rsp-webpack-4/package.json

@@ -23,7 +23,7 @@
     "@babel/cli": "^7.1.0",
     "@babel/preset-env": "^7.1.0",
     "@babel/preset-react": "^7.0.0",
-    "webpack": "4.19.1",
+    "webpack": "^4.46.0",
     "webpack-cli": "3.1.1",
     "webpack-dev-server": "3.1.8",
     "style-loader": "0.23.0",