Define the date format for git documents exactly as the default for `git log`

[Rafaeltheraven]

This is a patch for my earlier patch in #1099.

Some background: my own testing revealed that the documentation for java date formatting isn't completely correct and that dd does not always accept a non-zero padded day-of-month. I've subsequently delved into the git source code (the documentation is wrong but that's another story) and discovered that the default date format for git log has a non-zero-padded day-of-month and also optional timezone information depending on the users locale.

Technically, the date format for a git log message could be anything, but it can generally be assumed to be the default. Not sure how the CHAOSS team wants to deal with this possibility. Personally I think anyone who changes the default date format for their git log can be expected to know what they are doing and to troubleshoot the issue, but maybe it's good to document this somewhere.

The git log default formatting code is found here

[coveralls]

Pull Request Test Coverage Report for Build 4429163864

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.06%) to 82.319%

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Totals
Change from base Build 4428231357:	0.06%
Covered Lines:	9116
Relevant Lines:	11074

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💛 - Coveralls

[Rafaeltheraven]

@sduenas pinging you since you also looked at my previous PR.

[Rafaeltheraven]

Sorry, got distracted as the project for which I originally wrote these patches reached it's end. Wrote a changelog as requested

[zhquan]

Hi @Rafaeltheraven could you rebase your branch again and I will proceed to merge this PR