Duplicate operationIds don't cause validation errors

[YagoGG]

Running SwaggerParser.validate() on a Swagger file with operationId fields that aren't unique doesn't throw any exception.

The Swagger specification indicates that these fields must have unique values:

Unique string used to identify the operation. The id MUST be unique among all operations described in the API. Tools and libraries MAY use the operationId to uniquely identify an operation, therefore, it is recommended to follow common programming naming conventions.

(Emphasis mine)

[JamesMessinger]

Good suggestion. I'll plan to add that to the validation logic.

[marcelstoer]

I have a fix ready that I can create a PR for once the current issues with master are sorted out.