Laravel php artisan migrate：刷新语法错误

Question

This is the code:

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')->refrences('id')->on('users')->onDelete('cascade');
        });

And the error:

[Illuminate\Database\QueryException] SQLSTATE[HY000]: General error: 1 near ")": syntax error (SQL: create table "articles" ("id" integer not null primary key autoincrement, "user_id" int eger not null, "title" varchar not null, "body" text not null, "created_at"
datetime not null, "updated_at" datetime not null, "published_at" datetime not null, foreign key("user_id") references "users"() on delete cascade))

[PDOException] SQLSTATE[HY000]: General error: 1 near ")": syntax error

Any ideas?