Upgrade wepack-stream

Author: jakezatecky

package.json

@@ -56,7 +56,7 @@
     "react-dom": "^15.4.2",
     "react-test-renderer": "^15.5.4",
     "webpack": "^3.0.0",
-    "webpack-stream": "^3.2.0"
+    "webpack-stream": "^4.0.0"
   },
   "dependencies": {
     "classnames": "^2.2.5",