Skip definitions for well known types.

[RyogaK]

It seems that definitions of swagger.json for well known types are not necessary because well known types are already mapped to swagger's primitive types.

Could you confirm this?

[elliots]

Uhhm. I don't actually have this project set up to run at the moment, will this commit cause problems, or should i just accept it?

[RyogaK]

@elliots

It's not like your current project has problem, but it seems all of google.protobuf.* types will be converted to type: boolean, format: boolean and so on.
https://github.com/elliots/protoc-gen-twirp_swagger/blob/master/genswagger/template.go#L276

In other word, It seems XXXProtobufStringValue object and them don't need to be put in definitions.
At least, XXXProtobufXXXValue will be put in definitions now but it will not be referenced from other any objects.

Thank you for reading my poor English 🙇