Fix misuse of issue index for issue id.

- UpdateAssignee
- UpdateIssueMilestone
Avoid setting missing label/milestone/assignee ids

Label, milestone, assignee ids are not includes in post request, possible
js or form building bug.
Merge pull request #579 from TonyTsangHK/dev

Fix misuse of issue index for issue id.
update slack hook to use new format
Merge pull request #581 from compressed/slack_upd

update slack hook to use new format
Fix fork repo and macaron API broken