Add dependent destruction to issue links

app/models/issue.rb

@@ -35,8 +35,8 @@ class Issue < ActiveRecord::Base
   has_many :issue_assignees
   has_many :assignees, class_name: "User", through: :issue_assignees
 
-  has_many :referenced_issue_links, class_name: 'IssueLink', foreign_key: :source_id
-  has_many :referred_by_issue_links, class_name: 'IssueLink', foreign_key: :target_id
+  has_many :referenced_issue_links, class_name: 'IssueLink', foreign_key: :source_id, dependent: :destroy
+  has_many :referred_by_issue_links, class_name: 'IssueLink', foreign_key: :target_id, dependent: :destroy
 
   has_many :referenced_issues, through: :referenced_issue_links, source: :target
   has_many :referred_by_issues, through: :referred_by_issue_links, source: :source