Bump webpack-cli from 3.3.8 to 3.3.9 in /app (#215)

Bumps [webpack-cli](https://github.com/webpack/webpack-cli) from 3.3.8 to 3.3.9.
- [Release notes](https://github.com/webpack/webpack-cli/releases)
- [Changelog](https://github.com/webpack/webpack-cli/blob/v3.3.9/CHANGELOG.md)
- [Commits](webpack/webpack-cli@v3.3.8...v3.3.9)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

app/package-lock.json

@@ -23,7 +23,7 @@
     "postcss-loader": "^3.0.0",
     "style-loader": "^1.0.0",
     "webpack": "^4.40.2",
-    "webpack-cli": "^3.3.8"
+    "webpack-cli": "^3.3.9"
   },
   "scripts": {
     "webpack": "webpack"