chore(deps): bump nunjucks and gulp-nunjucks (#313)

Bumps [nunjucks](https://github.com/mozilla/nunjucks) to 3.2.4 and updates ancestor dependency [gulp-nunjucks](https://github.com/sindresorhus/gulp-nunjucks). These dependencies need to be updated together.


Updates `nunjucks` from 2.5.2 to 3.2.4
- [Release notes](https://github.com/mozilla/nunjucks/releases)
- [Changelog](https://github.com/mozilla/nunjucks/blob/master/CHANGELOG.md)
- [Commits](mozilla/nunjucks@v2.5.2...v3.2.4)

Updates `gulp-nunjucks` from 2.3.0 to 6.0.0
- [Release notes](https://github.com/sindresorhus/gulp-nunjucks/releases)
- [Commits](sindresorhus/gulp-nunjucks@v2.3.0...v6.0.0)

---
updated-dependencies:
- dependency-name: nunjucks
  dependency-version: 3.2.4
  dependency-type: indirect
- dependency-name: gulp-nunjucks
  dependency-version: 6.0.0
  dependency-type: direct:production
...

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Author: dependabot[bot]