Upgrade webpack and thread-loader

Author: Timer

packages/react-scripts/package.json

@@ -64,10 +64,10 @@
     "style-loader": "0.21.0",
     "svgr": "1.9.2",
     "sw-precache-webpack-plugin": "0.11.5",
-    "thread-loader": "1.1.5",
+    "thread-loader": "1.2.0",
     "uglifyjs-webpack-plugin": "1.2.5",
     "url-loader": "1.0.1",
-    "webpack": "4.8.3",
+    "webpack": "4.19.0",
     "webpack-dev-server": "3.1.7",
     "webpack-manifest-plugin": "2.0.3",
     "whatwg-fetch": "2.0.4"