Update python-slugify requirement from <=6.1.1,>=4.0 to >=4.0,<6.1.3 (#280)

Update python-slugify requirement from <=6.1.1,>=4.0 to >=4.0,<6.1.3 (#280)

Updates the requirements on [python-slugify](https://github.com/un33k/python-slugify) to permit the latest version.
- [Release notes](https://github.com/un33k/python-slugify/releases)
- [Changelog](https://github.com/un33k/python-slugify/blob/master/CHANGELOG.md)
- [Commits](https://github.com/un33k/python-slugify/compare/4.0.0...v6.1.2)

---
updated-dependencies:
- dependency-name: python-slugify
  dependency-type: direct:production
...

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