php artisan migrate:rollback is not working

<?php

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

class CreateUsersTable extends Migration {

    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('users', function(Blueprint $table)
        {
            $table->increments('id');
            $table->string('username')->unique();
            $table->string('email',200)->unique();
            $table->string('password', 255);
            $table->string('code');
            $table->integer('active');
            $table->string('remember_token');
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::drop('users');
    }

}