Add Support for OpenAPI v3.0

[fabsrc]

The OpenAPI (fka Swagger) was recently released. It includes several changes and new features which should also be useable in Swagger Combine.

This is only possible after Swagger Parser supports OpenAPI v3.0.

[shreyas-agnihotri]

APIDevTools/swagger-parser#72

[fabsrc]

Looks like Swagger Parser finally supports OpenAPI 3.0 which means we can start implementing support for OpenAPI 3.0 as well.

[ThaDaVos]

So what's the status on this?
Currently in the middle of a micro-services project using Express-Gateway and I would love to have a way to merge all OpenAPI 3 specs supplied by those microservices into one so Swagger UI or Postman can use it.

[ashiemke]

So after reading through the code and not understanding what was going on, I just experimented and this seems to work. Just drop an "openapi": "3.0.0" in place of the "swagger": "2.0" as the first line of the config, and everything seemed to work. Haven't tried to validate it or use for real, but looks promising 🤷‍♂️