chore(deps): update dependency webpack to v4.31.0 (#1856)

Author: renovate[bot]

package-lock.json

@@ -94,7 +94,7 @@
     "style-loader": "0.23.1",
     "supertest": "4.0.2",
     "url-loader": "1.1.2",
-    "webpack": "4.30.0",
+    "webpack": "4.31.0",
     "webpack-cli": "3.3.2",
     "ws": "6.2.1"
   },