add repository field to issue hook data

Created by: pjknkda

What does this do? Webhooks for issue now contains repository field which is in the same manner as comment events.

Why is this needed? Webhook provides the ability to update an external issue tracker, but there is no way to figure out the repository name of an issue when issue events are occured. Actually we can do it using project_id, but other webhook events provides both repository info and project_id.