Fix external wiki service

app/models/project.rb

@@ -89,11 +89,11 @@ class Project < ActiveRecord::Base
   has_one :redmine_service, dependent: :destroy
   has_one :custom_issue_tracker_service, dependent: :destroy
   has_one :gitlab_issue_tracker_service, dependent: :destroy
+  has_one :external_wiki_service, dependent: :destroy
 
   has_one :forked_project_link, dependent: :destroy, foreign_key: "forked_to_project_id"
 
   has_one :forked_from_project, through: :forked_project_link
-  has_one :external_wiki_service, dependent: :destroy
   # Merge Requests for target project should be removed with it
   has_many :merge_requests,     dependent: :destroy, foreign_key: 'target_project_id'
   # Merge requests from source project should be kept when source project was removed

app/models/service.rb

@@ -140,7 +140,7 @@ class Service < ActiveRecord::Base
       redmine
       custom_issue_tracker
       irker
-      external_wiki_service
+      external_wiki
     )
   end