Bumps [regex](https://github.com/rust-lang/regex) from 1.3.7 to 1.3.9.
- [Release notes](https://github.com/rust-lang/regex/releases)
- [Changelog](https://github.com/rust-lang/regex/blob/master/CHANGELOG.md)
- [Commits](rust-lang/regex@regex-1.3.7...1.3.9)

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