define the response payloads for the markdown endpoints

[shiftkey]

• endpoint scope: Markdown
• endpoint name : "Render an arbitrary Markdown document" and "Render a Markdown document in raw mode"
• route: /markdown and /markdown/raw
• documentation URL: https://developer.github.com/v3/markdown/

Current specification

routes/openapi/api.github.com/operations/markdown/render.json

Line 21 in 250db51

"responses": { "200": { "description": "response" } },

and

routes/openapi/api.github.com/operations/markdown/render-raw.json

Line 27 in 250db51

"responses": { "200": { "description": "response" } },

I expected

Something indicating the response is text/html, e.g:

"responses": {
  "200": {
    "description": "response",
    "content": {
      "text/html": {
        "schema": {
          "type": "string"
        }
      }
    }
  }
}

PR incoming, I can't seem to get the failing tests to pass locally but that's fine.