hgweb: open server logs in binary mode
This is consistent with when we're logging to stdout, so we don't have
to do something annoyingly complicated in the logging infrastructure.
Differential Revision: https://phab.mercurial-scm.org/D2294
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}