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"