Bump loader-utils from 1.2.3 to 1.4.2 in /gatsby (#1559)

Bumps [loader-utils](/~https://github.com/webpack/loader-utils) from 1.2.3 to 1.4.2.
- [Release notes](/~https://github.com/webpack/loader-utils/releases)
- [Changelog](/~https://github.com/webpack/loader-utils/blob/v1.4.2/CHANGELOG.md)
- [Commits](webpack/loader-utils@v1.2.3...v1.4.2)

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

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