build(deps-dev): Bump webpack-cli from 3.3.7 to 3.3.8 in /addon (#152)

Bumps [webpack-cli](https://github.com/webpack/webpack-cli) from 3.3.7 to 3.3.8.
- [Release notes](https://github.com/webpack/webpack-cli/releases)
- [Changelog](https://github.com/webpack/webpack-cli/blob/v3.3.8/CHANGELOG.md)
- [Commits](webpack/webpack-cli@v3.3.7...v3.3.8)

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

Author: dependabot-preview[bot]

addon/package-lock.json

@@ -13,7 +13,7 @@
     "eslint-plugin-no-unsanitized": "^3.0.2",
     "web-ext": "^3.1.1",
     "webpack": "^4.39.3",
-    "webpack-cli": "^3.3.7"
+    "webpack-cli": "^3.3.8"
   },
   "scripts": {
     "lint": "eslint src/*.js",