Reading a response with a status line like "HTTP/1.0  401 Unauthorized"
(with two spaces after the version) has been returning an error. Now the
extra space will be ignored.

Fixes #19989

Change-Id: I0c88a6ef7562ba80e2e2635be2070dd1b5b671a7
Reviewed-on: https://go-review.googlesource.com/40933Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>