كيف يمكنني حل الخطأ "Your requirements could not be resolved to an installable set of packages"

عندما أقوم بتشغيل composer install، أتلقى الخطأ التالي:

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

Problem 1
    - Installation request for symfony/event-dispatcher v4.0.1 -> satisfiable by symfony/event-dispatcher[v4.0.1].
    - symfony/event-dispatcher v4.0.1 requires php ^7.1.3 -> your PHP version (7.0.22) does not satisfy that requirement.
  Problem 2
    - Installation request for doctrine/instantiator 1.1.0 -> satisfiable by doctrine/instantiator[1.1.0].
    - doctrine/instantiator 1.1.0 requires php ^7.1 -> your PHP version (7.0.22) does not satisfy that requirement.
  Problem 3
    - Installation request for symfony/yaml v4.0.1 -> satisfiable by symfony/yaml[v4.0.1].
    - symfony/yaml v4.0.1 requires php ^7.1.3 -> your PHP version (7.0.22) does not satisfy that requirement.
  Problem 4
    - symfony/event-dispatcher v4.0.1 requires php ^7.1.3 -> your PHP version (7.0.22) does not satisfy that requirement.
    - symfony/http-kernel v3.4.1 requires symfony/event-dispatcher ~2.8|~3.0|~4.0 -> satisfiable by symfony/event-dispatcher[v4.0.1].
    - Installation request for symfony/http-kernel v3.4.1 -> satisfiable by symfony/http-kernel[v3.4.1].

و هذا ملف composer.json الخاص بي:

{
    "name": "laravel/laravel",
    "description": "The Laravel Framework.",
    "keywords": ["framework", "laravel"],
    "license": "MIT",
    "type": "project",
    "require": {
        "php": ">=5.6.4",
        "brozot/laravel-fcm": "^1.2",
        "guzzlehttp/guzzle": "^6.3",
        "laravel/framework": "5.4.*",
        "laravel/tinker": "~1.0",
        "maatwebsite/excel": "^2.1",
        "prettus/l5-repository": "^2.6",
        "pusher/pusher-php-server": "^3.0",
        "yajra/laravel-datatables-oracle": "8.*",
        "zizaco/entrust": "5.2.x-dev"
    },
    "require-dev": {
        "fzaninotto/faker": "~1.4",
        "mockery/mockery": "0.9.*",
        "phpunit/phpunit": "~5.7"
    },
    "autoload": {
        "classmap": [
            "database"
        ],
        "psr-4": {
            "App\\": "app/"
        },
        "files": [
            "app/Helper/HelperFunction.php"
        ]
    },
    "autoload-dev": {
        "psr-4": {
            "Tests\\": "tests/"
        }
    },
    "scripts": {
        "post-root-package-install": [
            "php -r \"file_exists('.env') || copy('.env.example', '.env');\""
        ],
        "post-create-project-cmd": [
            "php artisan key:generate"
        ],
        "post-install-cmd": [
            "Illuminate\\Foundation\\ComposerScripts::postInstall",
            "php artisan optimize"
        ],
        "post-update-cmd": [
            "Illuminate\\Foundation\\ComposerScripts::postUpdate",
            "php artisan optimize"
        ]
    },
    "config": {
        "preferred-install": "dist",
        "sort-packages": true,
        "optimize-autoloader": true
    }
}

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