Update dependency webpack-cli to v3.1.2 (#10)

Author: renovate[bot]

fixtures/app/package.json

@@ -12,6 +12,6 @@
   },
   "devDependencies": {
     "webpack": "4.20.2",
-    "webpack-cli": "3.0.7"
+    "webpack-cli": "3.1.2"
   }
 }

worker/package.json

@@ -13,7 +13,7 @@
     "css-to-js-sourcemap-core": "*",
     "resolve-from": "4.0.0",
     "webpack": "4.20.2",
-    "webpack-cli": "3.0.7"
+    "webpack-cli": "3.1.2"
   },
   "license": "MIT"
 }