fix: sort tags by commit order

[evanchaoli]

What does this do / why do we need it?

Currently git-chglog tool sorts tags by taggerdate or authordate, which may is not reliable.

For example, in our workflow, we may do the following:

Say, at day 1, our repo has the following commits:

commit-1
commit-2
commit-3

we tested commit-3, and tag it as stg-1. And commits keep growing:

commit-1
commit-2
commit-3 (stg-1)
commit-4
commit-5

At day 2, we tested commit-5, and we tag commit-5 as stg-2:

commit-1
commit-2
commit-3 (stg-1)
commit-4
commit-5 (stg-2)

At day 3, we release commit-3, so we tag commit-3 as prd-3:

commit-1
commit-2
commit-3 (stg-1, prd-1)
commit-4
commit-5 (stg-2)

At day 4, we want to see changes between last prod release (prd-1) and last stage release (stg-2), the expected result should be commit-4 and comit-5.

But current git-chglog cannot generate the correct change logs, because prd-1 is created later than stg-2.

How this PR fixes the problem?

This PR changes the way of tag sorting by date.

git log --oneline --decorate=short can generate commit history with tags on each commit, like:

f1bb0d1 (tag: stg-0.1.0-20210702-34-f1bb0d1, tag: dev-0.1.0-20210702-34-f1bb0d1) xxxx
312f701 xxxxxxx
4eb6495 (tag: stg-0.1.0-20210629-33-4eb6495, tag: dev-0.1.0-20210629-33-4eb6495) xxxx
f3c1554 xxxx
6f3a743 (tag: stg-0.1.0-20210624-32-6f3a743, tag: dev-0.1.0-20210624-32-6f3a743) xxxx
7ebc95f xxxx

We can sort tags with this order.

What should your reviewer look out for in this PR?

• Do we still need to keep Date field in Tag and RelateTag? I don't know if change log may refer to tag's date. If yes, we should keep it; otherwise tag date is useless then.

Check lists

• Test passed
• Coding style (indentation, etc)

Additional Comments (if any)

{Please write here}

Which issue(s) does this PR fix?

[coveralls]

Pull Request Test Coverage Report for Build 1123216732

• 30 of 37 (81.08%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.01%) to 76.819%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tag_reader.go	30	37	81.08%

Files with Coverage Reduction	New Missed Lines	%
tag_reader.go	1	92.81%

Totals
Change from base Build 1097947313:	0.01%
Covered Lines:	1869
Relevant Lines:	2433

---

💛 - Coveralls