fix InvalidDNSNameError when using ip inside url

[oyundev]

Works fine: get->url = "https://raw.githubusercontent.com/.../master/LICENSE-APACHE"
Fails: get->url = "https://151.101.0.133/.../master/LICENSE-APACHE"
with error: IoError(Custom { kind: Other, error: InvalidDNSNameError })

Requests should respect Host entry from request headers, following changes fixed it for me.

1.inside request.rs:
headers: HashMap<String, String>, => pub(crate) headers: HashMap<String, String>,
2.inside connection.rs:
let dns_name = &self.request.host; => let dns_name = self.request.headers.get("Host").unwrap_or(&self.request.host);

[neonmoe]

Thanks for the PR, and sorry for not responding earlier. I imagine I saw this in my inbox one morning and forgot.

The host header is actually set based on request.host, see Request::get_http_head. So generally you should not be setting the host header via the header API, instead you should be including the right host in the URL itself.

I'm not sure how this change fixed it for you, but the DNS handling should definitely be skipped if the host is an IP address, so I opened #34. In any case, I'll close this since I don't see how this would actually fix the problem.

If I misunderstood something, please reopen the PR, I'll gladly re-review it then.