Update nyholm/psr7 requirement from ^1.2 to ^1.3
Update nyholm/psr7 requirement from ^1.2 to ^1.3

Updates the requirements on [nyholm/psr7](https://github.com/Nyholm/psr7) to permit the latest version.
- [Release notes](https://github.com/Nyholm/psr7/releases)
- [Changelog](https://github.com/Nyholm/psr7/blob/master/CHANGELOG.md)
- [Commits](https://github.com/Nyholm/psr7/compare/1.2.0...1.3.0)

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