config: correct rootfs default

It doesn't make sense for us to not include a rootfs in
our default configuration -- as it means that we're providing an
invalid configuration.

Signed-off-by: Aleksa Sarai <asarai@suse.de>

Author: cyphar

generate/generate.go

@@ -41,7 +41,7 @@ func New() Generator {
 	spec := rspec.Spec{
 		Version: rspec.Version,
 		Root: &rspec.Root{
-			Path:     "",
+			Path:     "rootfs",
 			Readonly: false,
 		},
 		Process: &rspec.Process{