Laravel Composer 看到错误的 PHP 版本

I'm trying to install an older Laravel Project.

当我跑的时候 composer install I get the following error

This package requires php >=5.6.4 but your PHP version (5.5.35) does not satisfy that requirement.

当我跑的时候

php -v

I get the following result

PHP 7.1.10 (cli) (built: Oct 12 2017 14:00:12) ( ZTS )

这是我的Composer.json的内容

{
    "name": "laravel/laravel",
    "description": "The Laravel Framework.",
    "keywords": ["framework", "laravel"],
    "license": "MIT",
    "type": "project",
    "require": {
        "php": ">=5.6.4",
        "doctrine/dbal": "^2.6",
        "guzzlehttp/guzzle": "^6.3",
        "intervention/image": "^2.4",
        "intervention/imagecache": "^2.3",
        "laravel/framework": "5.4.*",
        "laravel/tinker": "~1.0",
        "laravelcollective/html": "^5.4",
        "maatwebsite/excel": "^2.1",
        "sentry/sentry-laravel": "^0.8.0",
        "spatie/laravel-glide": "^3.2",
        "spatie/laravel-permission": "^2.6",
        "spatie/laravel-pjax": "^1.3"
    },
    "require-dev": {
        "fzaninotto/faker": "~1.4",
        "mockery/mockery": "0.9.*",
        "phpunit/phpunit": "~5.7"
    },
    "autoload": {
        "classmap": [
            "database"
        ],
        "psr-4": {
            "App\\": "app/"
        }
    },
    "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
    }
}

这个项目怎么可能认为我运行了PHP5.6？

非常感谢.