fetch-upstream-resources: use wget --directory-prefix
fetch-upstream-resources: use wget --directory-prefix

When using Gnu Wget, the `--directory-prefix` option automatically
creates the specified path if it doesn't exist.

Note that this does not work when using the busybox version
of Wget (but we're not using that in our Dockerfile).

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

docker/docker.github.io,docker/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io,londoncalling/docker.github.io,londoncalling/docker.github.io,londoncalling/docker.github.io,thaJeztah/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io,thaJeztah/docker.github.io,londoncalling/docker.github.io,londoncalling/docker.github.io