Allow IP tuple for host #152

[essen]

I don't think this is working:

2> application:ensure_all_started(gun).     
{ok,[crypto,asn1,public_key,ssl,cowlib,ranch,gun]}
3> {ok, C} = gun:open({64,233,184,138}, 80).
{ok,<0.91.0>}
4> gun:get(C, "/").
#Ref<0.1855665614.3723493377.109334>
5> 
=ERROR REPORT==== 7-May-2018::13:44:18 ===
Bad value on output port 'tcp_inet'

It's probably trying to send a tuple for the Host header.

[seudin]

It will working with header <<"host">>.

gun:get(C, "/", [{<<"host">>, ["64.233.184.138"]}]).

I will update PR for no host header.

[seudin]

The PR is updated.

[essen]

Merged locally, pushed in a few. Thanks!