Bump laravel/framework from 5.8.35 to 6.18.43

Bumps [laravel/framework](https://github.com/laravel/framework) from 5.8.35 to 6.18.43.
- [Release notes](https://github.com/laravel/framework/releases)
- [Changelog](https://github.com/laravel/framework/blob/8.x/CHANGELOG-6.x.md)
- [Commits](laravel/framework@v5.8.35...v6.18.43)

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

composer.json

@@ -21,7 +21,7 @@
     "php": "^7.1.3",
     "42coders/document-templates": "*",
     "fideloper/proxy": "^4.0",
-    "laravel/framework": "5.8.*",
+    "laravel/framework": "6.18.*",
     "laravel/tinker": "^1.0"
   },
   "require-dev": {