No Content-Type header?

[weakish]

It seems that the Content-Type header is absent.

http --headers https://docsify.now.sh/
HTTP/1.1 200 OK
Accept-Ranges: bytes
Connection: keep-alive
Content-Length: 6768
Date: Fri, 22 Nov 2019 15:56:55 GMT
X-Now-Instance: 1225455044
cache-control: s-maxage=0
server: now
strict-transport-security: max-age=63072000
x-now-id: tpe1:gxhtn-1574438215153-518509923d3f
x-now-trace: tpe1,sfo1

This causes w3m to display the plain HTML source without rendering it.