Fix strategie db increment when primary key is uuid.

[chiaretto]

Problem

Error on strategie dbIncrement when primary key is uuid.

Solution

Change order by to filed value for best result. Now works independently of the primary key

[coveralls]

Pull Request Test Coverage Report for Build 42

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.1%) to 92.0%

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Totals
Change from base Build 38:	-0.1%
Covered Lines:	44
Relevant Lines:	47

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💛 - Coveralls

[igortrinidad]

Thanks @chiaretto

This fix for the dbIncrement strategy fixed the error 'duplicate entry' when the model has uuid primary and trying to update with one slug that already exists...

[thetutlage]

The next rewrite for v5 takes inspiration for this PR handle this use case. Since, I have rewritten the entire package, it is impossible to merge this PR. :)