Convert variable names to camel case in PHPDoc

[MAILPOET-1796]

lib/Models/StatisticsClicks.php

@@ -5,10 +5,10 @@ namespace MailPoet\Models;
 use DateTimeInterface;
 
 /**
- * @property int $newsletter_id
- * @property int $subscriber_id
- * @property int $queue_id
- * @property int $link_id
+ * @property int $newsletterId
+ * @property int $subscriberId
+ * @property int $queueId
+ * @property int $linkId
  * @property int $count
  */
 class StatisticsClicks extends Model {