Feature comments: notification missing when updating an existing comment

[ddu-rodwolf]

/github subscribe owner/repo comments sends notification to the Slack "GitHub" app channel (evtl. in a thread GitHub) when:

• new comment
• delete comment
  but not if a comment has been further edited/modified.
  Would be definitively very useful to get such kind of notification, to avoid missing an evtl. important update on that comment.