Bump phpstan/phpstan from 1.1.1 to 1.2.0

Bumps [phpstan/phpstan](https://github.com/phpstan/phpstan) from 1.1.1 to 1.2.0.
- [Release notes](https://github.com/phpstan/phpstan/releases)
- [Changelog](https://github.com/phpstan/phpstan/blob/master/CHANGELOG.md)
- [Commits](phpstan/phpstan@1.1.1...1.2.0)

---
updated-dependencies:
- dependency-name: phpstan/phpstan
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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