Update phpspec/prophecy requirement from ^1.14 to ^1.15
Update phpspec/prophecy requirement from ^1.14 to ^1.15

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/1.14.0...v1.15.0)

---
updated-dependencies:
- dependency-name: phpspec/prophecy
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
slimphp/Slim-Csrf,akrabat/Slim-Csrf