How to fix error Parse error: syntax error, unexpected '=' in Cell.php

I've deployed my laravel source which integrated maatwebsite package inside, i have some export excel in my project. It works fine in the xampp localhost, but when i deploy it to the virtual server, it always return error:

message: "Parse error: syntax error, unexpected '='"
exception: "Symfony\Component\Debug\Exception\FatalThrowableError"
file: "/var/www/src/vendor/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Cell/Cell.php"
line: 517

I set up php7.1 and my require composer.json:

"require": {
        "php": ">=7.0.0",
        "ext-json": "*",
        "fideloper/proxy": "~3.3",
        "laravel/framework": "5.5.*",
        "laravel/tinker": "~1.0",
        "laravelcollective/html": "^5.4.0",
        "maatwebsite/excel": "^3.1"
    }

Someone can tell me how to fix this problem???

via Chebli Mohamed