Content-type of swagger.json should be application/json

[provegard]

Expected Behavior

Content-type for the swagger.json endpoint is application/json (possibly with charset).

Actual Behavior

Content-type for the swagger.json endpoint is text/plain; charset=utf-8.

Steps to Reproduce the Problem

1. Build a small application that uses Nancy.Swagger
2. Open DevTools in Chrome (or similar) and enable network recording
3. Visit the swagger.json endpoint

Specifications

• Version: 2.2.56-alpha