fixup. fix scriptlet string conversion impl

[juliusl]

📜 Checklist

• [ ] Commits are cleanly separated and have useful messages
• [ ] A changelog entry or entries has been added to CHANGELOG.md
• [ ] Documentation is thorough
• [ ] Test coverage is excellent and passes
• [ ] Works when tests are run --all-features enabled

[juliusl]

@dralley When I was working on the cargo-generate-rpm pr I noticed the conversion impl I picked could be improved. Would it be okay to merge this?