Php 例外情况'；PDO异常'；带有消息'；SQLSTATE[HY000]：一般错误：1接近“1”）&引用；拉维尔

我正在学习Laravel5关于laracast的教程，我发现了这个错误

异常“PDOException”，消息为“SQLSTATE[HY000]：一般错误：1近”）：

您在“refresents（'id'）上有一个输入错误。您的迁移应该如下所示：

<?php

use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class Test extends Migration {

/**
 * Run the migrations.
 *
 * @return void
 */
    public function up()
    {
        Schema::create('articles', function(Blueprint $table)
        {
            $table->increments('id');
            $table->integer('user_id')->unsigned();
            $table->string('title');
            $table->text('body');
            $table->timestamps();
            $table->timestamp('published_at');

            $table->foreign('user_id')
            ->references('id')
            ->on('users')
            ->onDelete('cascade');
        });
     }

/**
 * Reverse the migrations.
 *
 * @return void
 */
public function down()
{
    Schema::table('articles', function(Blueprint $table){
        $table->dropForeign('articles_user_id_foreign');
        });
        Schema::drop('articles');
    }

}

<?php

use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class Test extends Migration {

/**
 * Run the migrations.
 *
 * @return void
 */
    public function up()
    {
        Schema::create('articles', function(Blueprint $table)
        {
            $table->increments('id');
            $table->integer('user_id')->unsigned();
            $table->string('title');
            $table->text('body');
            $table->timestamps();
            $table->timestamp('published_at');

            $table->foreign('user_id')
            ->references('id')
            ->on('users')
            ->onDelete('cascade');
        });
     }

/**
 * Reverse the migrations.
 *
 * @return void
 */
public function down()
{
    Schema::table('articles', function(Blueprint $table){
        $table->dropForeign('articles_user_id_foreign');
        });
        Schema::drop('articles');
    }

}