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>

env/linux-x86-std-kube/Dockerfile

@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style
 # license that can be found in the LICENSE file.
 
-FROM debian:wheezy
+FROM debian:jessie
 MAINTAINER golang-dev <golang-dev@googlegroups.com>
 
 ENV DEBIAN_FRONTEND noninteractive