wrong content type for request

```sh
curl -d "@example.json" -H "Content-Type:application/json;charset=utf-8" "http://fox-demo.aksw.org/fox" -vvv
```

gives

```
* Trying 139.18.2.38...
* TCP_NODELAY set
* Connected to fox-demo.aksw.org (139.18.2.38) port 80 (#0)
> POST /fox HTTP/1.1
> Host: fox-demo.aksw.org
> User-Agent: curl/7.58.0
> Accept: */*
> Content-Type:application/json;charset=utf-8
> Content-Length: 269
>
* upload completely sent off: 269 out of 269 bytes
< HTTP/1.1 200 OK
< Date: Thu, 11 Oct 2018 16:19:25 GMT
< Server: Jetty(9.3.6.v20151106)
< Content-Type: application/x-turtle;charset=utf-8
< Transfer-Encoding: chunked
<
{
"@graph" : [ {
"@id" : "_:b0",
"@type" : [ "foxo:NamedEntityRecognition", "prov:Activity" ],
"endedAtTime" : "2018-10-11T18:19:25.590+02:00",
"generated"...
```

Content-Type: application/x-turtle;charset=utf-8 should be something "json-ld"

Start at the POST /fox endpoint and reproduce the request with the provided curl command, checking the response body and Content-Type header. Done means the JSON-LD response is labelled with the appropriate JSON-LD media type rather than application/x-turtle.

Written by the indexing model from the issue text.