Update dependency webpack to v4.31.0 (reactjs#797)

Author: renovate[bot]

src/React.Core/Resources/babel-legacy/package-lock.json

@@ -12,7 +12,7 @@
     "babel-preset-es2015": "6.24.1",
     "babel-preset-stage-0": "6.24.1",
     "babel-standalone": "6.26.0",
-    "webpack": "4.30.0",
+    "webpack": "4.31.0",
     "webpack-cli": "3.3.0"
   },
   "author": "",