Update x86_64 requirement from 0.7.2 to 0.8.1
Update x86_64 requirement from 0.7.2 to 0.8.1

Updates the requirements on [x86_64](https://github.com/rust-osdev/x86_64) to permit the latest version.
- [Release notes](https://github.com/rust-osdev/x86_64/releases)
- [Changelog](https://github.com/rust-osdev/x86_64/blob/master/Changelog.md)
- [Commits](https://github.com/rust-osdev/x86_64/compare/0.7.2...v0.8.1)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
bemeurer/daedalos