larave5.1 集成 MongoDB 实例化报错问题?

提示错误Unsupported driver [mongodb]

已在composer.json 中加入 "jenssegers/mongodb":"3.0.*"
app.php 中加入 Jenssegers\Mongodb\MongodbServiceProvider::class,
database.php中配置如下

         'mongodb' => [
            'driver'   => 'mongodb',
            'host'     => env('MONGO_DB_HOST', 'localhost'),
            'port'     => env('MONGO_DB_PORT', 27017),
            'database' => env('MONGO_DB_DATABASE', 'sistalk_demo'),
            //'username' => env('DB_USERNAME'),
            //'password' => env('DB_PASSWORD'),
            'options'  => [
                'database' => 'laravel_project_db'
            ]
        ],

    控制器代码如下

    ```
    $status = DB::connection('mongodb');
    var_dump($status);
    ```