env: change linux-x86-std-kube to debian jessie

Updates golang/go#20382

Change-Id: I87ac8f53278f1624232b3239e61b60cc2ee341ca
Reviewed-on: https://go-review.googlesource.com/43535
Reviewed-by: Sarah Adams <shadams@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed