Wrong accept header when making external reference calls with yaml

Q&A (please complete the following information)

• OS: Windows 10
• Environment: Chrome Version 76.0.3809.100
• Method of installation: CDN
• Swagger-Client version: 3.9.2
• Swagger/OpenAPI version: OpenAPI 3.0

This zip contains two yaml files. api1.yaml and api2.yml.

Open api1.yaml and then expand the GET box for /test-api-1
If you are serving up these files on a webserver, you'll notice the accept header in the request is application/json.

This causes my IIS server to return an error since it associates *.yaml with application/yaml.

If if I associate *.yaml with application/json (which is a hack), then swagger will still complain because it will get a content-type response of application/json and then not be able to parse the yaml which it thinks is json.

The fix is very easy, we just need to change this line
https://github.com/swagger-api/swagger-js/blob/master/src/resolver.js#L16

to

Accept: 'application/json, application/yaml'

Start with src/resolver.js at the referenced line and reproduce the request using the api1.yaml and api2.yml files from the attached archive. Verify that external YAML references receive an Accept header supporting YAML and that the returned YAML is still parsed correctly in the Swagger UI flow.