Added application/json;charset="utf-8" as accepted content.

I got an issue when I deployed swagger core on JBoss7+Resteasy 2.5.7.

During initialization (downloading api-docs form endpoint on JBoss7) the request was rejected by JBoss server because Restasy framework said that it can't produce accepted content type.
The servlet from swagger-core told that it produces application/json;charset="utf-8" and client said that it can accept application/json. So I'm adding application/json;charset="utf-8" as accepted to those requests.