Update slim/slim requirement from ^4.5 to ^4.7

Updates the requirements on [slim/slim](https://github.com/slimphp/Slim) to permit the latest version.
- [Release notes](https://github.com/slimphp/Slim/releases)
- [Changelog](https://github.com/slimphp/Slim/blob/4.x/CHANGELOG.md)
- [Commits](slimphp/Slim@4.5.0...4.7.0)

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

composer.json

@@ -20,7 +20,7 @@
     "require": {
         "php": "^7.2",
         "psr/http-message": "^1.0",
-        "slim/slim": "^4.5",
+        "slim/slim": "^4.7",
         "twig/twig": "^3.1"
     },
     "require-dev": {