I guess that might be it, but it doesn’t seem to be working. I see these headers when I curl the URL. I’d expect an explicit Content-Type to be returned.
< HTTP/1.1 200 OK
< Date: Mon, 30 Apr 2018 15:00:38 GMT
< Server: Apache
< Last-Modified: Mon, 30 Apr 2018 08:45:23 GMT
< ETag: "b1a1ade-3a73-56b0cdfe70151"
< Accept-Ranges: bytes
< Content-Length: 14963
< Vary: Accept-Encoding,User-Agent