Fix OpenAPI examples

[ohtake]

There are breaking changes in go-openapi/spec#113.
This pull request fixes them.

$ cd examples
$ go build restful-openapi.go
# command-line-arguments
.\restful-openapi.go:157:5: cannot use promoted field ContactInfoProps.Name in struct literal of type spec.ContactInfo
.\restful-openapi.go:158:5: cannot use promoted field ContactInfoProps.Email in struct literal of type spec.ContactInfo
.\restful-openapi.go:159:5: cannot use promoted field ContactInfoProps.URL in struct literal of type spec.ContactInfo
.\restful-openapi.go:162:5: cannot use promoted field LicenseProps.Name in struct literal of type spec.License
.\restful-openapi.go:163:5: cannot use promoted field LicenseProps.URL in struct literal of type spec.License

[emicklei]

thank you for contributing. the examples were made in the time we did not have Go modules. I will merge your request but also will introduce Go module support here to at least document what version is expected.