create records using ModelFactory's "createMany" sequentially

[MZanggl]

Proposed changes

Adresses issue #489 in which "createMany" on a model factory creates records with autoincrement in random order. The content of the method is now identical with the way it is done in the DatabaseFactory.

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

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• I have read the CONTRIBUTING doc
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works.
• I have added necessary documentation (if appropriate)

Further comments

Not sure if the Promise.all was there for performance reasons. Alternatively I can sort the array like I mentioned in the issue originally.

[coveralls]

Coverage increased (+0.009%) to 96.515% when pulling 99f9693 on MZanggl:bugfix/create-many-sorted into 6cd666d on adonisjs:develop.

[thetutlage]

Makes sense 😄