Laravel relationship error in migration

I am trying to make two tables relationship in laravel. But i can't understand why i'm getting error "errno: 150 "Foreign key constraint is incorrectly formed"". please check my migration code below.

items table

public function up()
{
    Schema::create('items', function (Blueprint $table) {
        $table->increments('id');
        $table->integer('category_id')->unsigned();
        $table->string('name');
        $table->decimal('price',5,2);
        $table->integer('count_left')->default(0);
        $table->timestamps();

        $table->foreign('category_id')->references('id')->on('categories');
    });
}

categories

public function up()
{
    Schema::create('categories', function (Blueprint $table) {
        $table->increments('id');
        $table->string('name')->unique();
        $table->timestamps();
    });
}

via Chebli Mohamed