Expunge user:pass@... from Host header.

In verbose mode, the basic auth user and password would show up in colored
output reporting the Host header, as reported in https://github.com/jkbr/httpie/issues/169

Similar code is used at https://github.com/jkbr/httpie/blob/4fe3deb9d916023b3bffe60e0d655216bcb9276a/httpie/sessions.py#L35