pw: avoid double slash in URIs

kernel.org's patchwork is sensitive to double slashes.
While ozlabs would happily respond to:

https://patchwork.ozlabs.org/api/1.1//series/$id

kernel.org will return a 404 unless we remove the double
slash after the API version.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>