Update swagger parser to 2.0.23

[wing328]

Update swagger parser to 2.0.23.

Reviewed the release note and the changes are pretty minor: https://github.com/swagger-api/swagger-parser/releases

cc @OpenAPITools/generator-core-team

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[wing328]

FYI. Tried updating to 2.0.24 but one or two unit tests failed.