Since increments() creates an unsigned integer column, you need to define the foreign key column as unsigned integer too.

Default migrations in Laravel 6+ use bigIncrements(), so you need to use unsignedBigInteger() method:

$table->unsignedBigInteger('order_id');
https://laravel.com/docs/6.x/migrations#foreign-key-constraints

For default migrations in older versions of Laravel use unsignedInteger() method:

$table->unsignedInteger('order_id');
Or:

$table->integer('order_id')->unsigned();