Update bitvec requirement from 0.18 to 0.19
Update bitvec requirement from 0.18 to 0.19

Updates the requirements on [bitvec](https://github.com/myrrlyn/bitvec) to permit the latest version.
- [Release notes](https://github.com/myrrlyn/bitvec/releases)
- [Changelog](https://github.com/myrrlyn/bitvec/blob/develop/CHANGELOG.md)
- [Commits](https://github.com/myrrlyn/bitvec/compare/v0.18.0...v0.19.0)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
sunjay/turtle,sunjay/turtle,sunjay/turtle