error.md

Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - The requested package graham-campbell/markdown could not be found in any version, there may be a typo in the package name.

Potential causes:
 - A typo in the package name
 - The package is not available in a stable-enough version according to your minimum-stability setting
   see <https://getcomposer.org/doc/04-schema.md#minimum-stability> for more details.

Read <https://getcomposer.org/doc/articles/troubleshooting.md> for further common problems.
Macbook-van-Tim:Armoedebestrijding tim$ 

Composer file:

{
    "name": "laravel/laravel",
    "description": "The Laravel Framework.",
    "keywords": ["framework", "laravel"],
    "license": "MIT",
    "type": "project",
    "minimum-stability": "dev",
    "require": {
        "php": ">=7.0.0",
        "activismebe/database-layering": "^0.27.0",
        "activismebe/laravel-form-helpers": "^1.1",
        "cybercog/laravel-ban": "^3.0",
        "fideloper/proxy": "~3.3",
        "laracasts/flash": "^3.0",
        "laravel/framework": "5.5.*",
        "laravel/tinker": "~1.0",
        "spatie/laravel-permission": "^2.7",
        "graham-campbell/markdown": "^8.0"
    },
    "require-dev": {
        "filp/whoops": "~2.0",
        "fzaninotto/faker": "~1.4",
        "mockery/mockery": "0.9.*",
        "phpunit/phpunit": "~6.0"
    },
    "autoload": {
        "classmap": [
            "database/seeds",
            "database/factories"
        ],
        "psr-4": {
            "App\\": "app/"
        }
    },
    "autoload-dev": {
        "psr-4": {
            "Tests\\": "tests/"
        }
    },
    "extra": {
        "laravel": {
            "dont-discover": [
            ]
        }
    },
    "scripts": {
        "post-root-package-install": [
            "@php -r \"file_exists('.env') || copy('.env.example', '.env');\""
        ],
        "post-create-project-cmd": [
            "@php artisan key:generate"
        ],
        "post-autoload-dump": [
            "Illuminate\\Foundation\\ComposerScripts::postAutoloadDump",
            "@php artisan package:discover"
        ]
    },
    "config": {
        "preferred-install": "auto",
        "sort-packages": true,
        "optimize-autoloader": true
    }
}