Problems making a composer update in laravel?

I am finding a problem that is too weird, I am working with laravel 5.2, I have the version of php 7.2, when I do the command "composer update" I get an error

this is my composer.json

{
    "name": "laravel/laravel",
    "description": "The Laravel Framework.",
    "keywords": ["framework", "laravel"],
    "license": "MIT",
    "type": "project",
    "require": {
        "php": ">=5.5.9",
        "barryvdh/laravel-dompdf": "0.6.*",
        "laravel/framework": "5.2.*",
        "laravelcollective/html": "5.2.*",
        "intervention/image": "^2.3",
        "appzcoder/crud-generator": "^1.0",
        "guzzlehttp/guzzle": "~6.0",
        "dnetix/redirection": "^0.4.2"
    },
    "require-dev": {
        "fzaninotto/faker": "~1.4",
        "mockery/mockery": "0.9.*",
        "phpunit/phpunit": "~4.0",
        "symfony/css-selector": "2.8.*|3.0.*",
        "symfony/dom-crawler": "2.8.*|3.0.*"
    },
    "autoload": {
        "classmap": [
            "database"
        ],
        "psr-4": {
            "Banco2\": "app/"
        }
    },
    "autoload-dev": { 
        "classmap": [
            "tests/TestCase.php"
        ]
    },
    "scripts": {
        "post-root-package-install": [
            "php -r \"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"
    }
}

Thank you very much