从 Laravel 5+ 中的数据库中删除列

我有一个博客，articles table Schema的定义如下:

public function up()
{
    Schema::create('articles', function (Blueprint $table) {
        $table->increments('id');
        $table->integer('user_id')->unsigned();
        $table->string('title');
        $table->string('thumb')->nullable();
        $table->text('excerpt');
        $table->text('body');
        $table->string('slug')->unique();
        $table->integer('comment_count')->unsigned()->default(0);
        $table->integer('view_count')->unsigned()->default(0);
        $table->timestamps();
        $table->softDeletes();
}

public function down()
{
    Schema::drop('articles');
}

我希望在不丢失表中现有数据的情况下删除列comment_count和view_count

我定义了一个新的迁移，如下所示:

class RemoveCommentViewCount extends Migration
{
    public function up()
    {
        //nothing here
    }

    public function down()
    {
        Schema::table('articles', function($table) {
           $table->dropColumn('comment_count');
           $table->dropColumn('view_count');
       });
   }
}

and I did php artisan migrate . It did migrate successfully, but the two columns are not dropped.

What am I doing wrong? How can I drop those columns without losing the existing data in the table?