Update phpspec/prophecy requirement from ^1.11 to ^1.12
Update phpspec/prophecy requirement from ^1.11 to ^1.12

Updates the requirements on [phpspec/prophecy](https://github.com/phpspec/prophecy) to permit the latest version.
- [Release notes](https://github.com/phpspec/prophecy/releases)
- [Changelog](https://github.com/phpspec/prophecy/blob/master/CHANGES.md)
- [Commits](https://github.com/phpspec/prophecy/compare/1.11.0...1.12.1)

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