http.server: fix typo

Introduced in:
> commit e7f888ccadce6ec68a6da783282bb342785d763d
> Author: Emil Renner Berthing <esmil@mailme.dk>
> Date:   Mon Aug 19 01:10:11 2013 +0200
>
>     http: factor out response module

Signed-off-by: Asbjørn Sloth Tønnesen <ast@fiberby.dk>