feat(webhook): display article reply's time instead of replies' time

[MrOrz]

Because

• reply time can be earlier than article time, leading to confusion
• websites show article reply time in article detail

Thus we should display the time of article-reply in the place where we display reply times to reduce confusion

[coveralls]

Pull Request Test Coverage Report for Build 7466516231

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.03%) to 87.823%

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Totals
Change from base Build 7465466044:	0.03%
Covered Lines:	1029
Relevant Lines:	1131

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💛 - Coveralls

[MrOrz]

Tested on staging on wednesday, merging