public function up()
{
    Schema::create('role_user', function (Blueprint $table) {
        $table->integer('user_id')->unsigned();
        $table->integer('role_id')->unsigned();
        $table->foreign('user_id')->references('id')->on('users')
            ->onDelete('cascade');
        $table->foreign('role_id')->references('id')->on('roles')
            ->onDelete('cascade');
    });
}