Update mikey179/vfsStream requirement from 1.6.5 to 1.6.6
Update mikey179/vfsStream requirement from 1.6.5 to 1.6.6

Updates the requirements on [mikey179/vfsStream](https://github.com/bovigo/vfsStream) to permit the latest version.
- [Release notes](https://github.com/bovigo/vfsStream/releases)
- [Changelog](https://github.com/bovigo/vfsStream/blob/master/CHANGELOG.md)
- [Commits](https://github.com/bovigo/vfsStream/compare/v1.6.5...v1.6.6)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
adrianclay/php-git