Bump loader-utils from 2.0.2 to 2.0.4 in /webext

Bumps [loader-utils](https://github.com/webpack/loader-utils) from 2.0.2 to 2.0.4.
- [Release notes](https://github.com/webpack/loader-utils/releases)
- [Changelog](https://github.com/webpack/loader-utils/blob/v2.0.4/CHANGELOG.md)
- [Commits](webpack/loader-utils@v2.0.2...v2.0.4)

---
updated-dependencies:
- dependency-name: loader-utils
  dependency-type: indirect
...

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