added missing event prefix in collection

Author: niravkrish

app/code/Magento/SalesRule/Model/ResourceModel/Rule/Collection.php

@@ -29,6 +29,20 @@ class Collection extends \Magento\Rule\Model\ResourceModel\Rule\Collection\Abstr
      */
     protected $_associatedEntitiesMap;
 
+    /**
+     * Event prefix
+     *
+     * @var string
+     */
+    protected $_eventPrefix = 'salesrule_rule_collection';
+
+    /**
+     * Event object
+     *
+     * @var string
+     */
+    protected $_eventObject = 'rule_collection';
+
     /**
      * @var \Magento\SalesRule\Model\ResourceModel\Rule\DateApplier
      * @since 100.1.0