content-type in http request

[reza....@pintapin.com]

How can I add content-type to request header

I use addHeader(Rawcode) in my code but it always ignore it and show this error

Explicitly set HTTP header 'content-type: application/json' is ignored, illegal RawHeader

```

val responseFuture: Future[HttpResponse] =
  Http().singleRequest(HttpRequest(HttpMethods.PUT, uri = "http://localhost/log/", entity = HttpEntity(RealData.fakeData).withContentType(ContentTypes.`application/json`)  ).withHeaders(RawHeader("x-auth-id",RealData.xAuthId),RawHeader("lang","fa"),RawHeader("content-type","application/json")))

```