Bump minimatch and gulp in /web/themes/custom/custom_theme

Bumps [minimatch](https://github.com/isaacs/minimatch) to 3.0.4 and updates ancestor dependency [gulp](https://github.com/gulpjs/gulp). These dependencies need to be updated together.


Updates `minimatch` from 0.2.14 to 3.0.4
- [Release notes](https://github.com/isaacs/minimatch/releases)
- [Commits](isaacs/minimatch@v0.2.14...v3.0.4)

Updates `gulp` from 3.9.1 to 4.0.2
- [Release notes](https://github.com/gulpjs/gulp/releases)
- [Changelog](https://github.com/gulpjs/gulp/blob/master/CHANGELOG.md)
- [Commits](gulpjs/gulp@v3.9.1...v4.0.2)

---
updated-dependencies:
- dependency-name: minimatch
  dependency-type: indirect
- dependency-name: gulp
  dependency-type: direct:development
...

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Author: dependabot[bot]