Bump phpspec/prophecy from 1.6.2 to 1.8.0

Bumps [phpspec/prophecy](https://github.com/phpspec/prophecy) from 1.6.2 to 1.8.0.
- [Release notes](https://github.com/phpspec/prophecy/releases)
- [Changelog](https://github.com/phpspec/prophecy/blob/master/CHANGES.md)
- [Commits](phpspec/prophecy@v1.6.2...1.8.0)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Author: dependabot-support