fix(lib): fix enum array on model properties

[nartc]

fix #808

PR Checklist

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• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: #808

What is the new behavior?

@ApiProperty({ enum: EnumType, enumName: 'EnumType', isArray: true }) should produce the correct schema

{
   "type": "array",
   "items": {
       "$ref$": "#/components/schemas/EnumType"
    }
}

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[kamilmysliwiec]

Thank you ❤️